Which is the best smartphone between OnePlus 2 and Samsung Galaxy S6 ?

Well, it is a tricky question indeed. A brief comparison between the Samsung Galaxy S6 and One Plus Two yields the following inferences-
Design and Build
In terms of build, both the devices tend to look premium. One Plus Two has a metal frame and steel accents. The rear cover is made of "real Wood". The finger print scanner included in the Home button has a touch type implementation. Then there is an Alert Slider which lets you set notification preferences without the need to wake up the phone. This is the first time introduction on an Android device. The Galaxy S6 features a metal and glass unibody design. It has the standard Samsung look and feel.
One Plus Two is bigger than Galaxy S6. So, as such, the S6 will offer more handling comfort than its competitor.
Display
One Plus One comes with a 5.5 inch full HD display with an impressive pixel density of 401 ppi. The in-cell IPS display ensures better viewing angles. It does have a good outdoor visibility. Galaxy S6 has a smaller 5.1 inch screen, but has a better display by having a quad HD resolution. It offers a massive 577 ppi pixel density. The AMOLED screen provides amazing colors.

Hardware
One Plus Two is powered by , Qualcomm Snapdragon 810 Octacore processor v2.1, with a clock speed of 1.8 GHz. It comes with 3 or 4 GB of RAM depending on the internal storage variant. The Snapdragon processor has some overheating issues reported, but One Plus claims that it has been working closely with the Qualcomm engineers to make the phone " cooler than ever".
Galaxy S6 skipped the Snapdragon processor and has employed the in house Octacore Exynos processor which appears to be good move. It offers an onboard RAM of 3 GB. The processor has been better optimized to offer lag free operation.
One Plus has two memory variants in 16 and 64 GB, while Galaxy S6 comes in an additional variant of 128 GB. Both of them lack expandable memory though.
Camera
The Galaxy S6 has a 16 MP rear camera with improved Optical Image Stabilisation. The HDR feature has received a facelift. It boasts of a Tracking Focus feature which tracks moving objects while shooting.
The One Plus Two comes with a 13 MP camera with f/2.0 aperture. It has a Laser Auto Focus system which can focus in just 0.3 seconds. It supports 4K video recording.
Software
One Plus Two runs on Oxygen OS which is developed by One Plus. The software is based on Android Lollipop 5.0. It has a near stock android experience which is refreshing. It does not come with any fancy feature apart from a few gesture controls.
Galaxy S6 runs on the same Android Lollipop 5.0 with customization from TouchWiz. The TouchWiz skin has been optimized for faster performance than that used to be earlier. It is much leaner now with less bloatware.
What I would think
I do not think either of them play any one upmanship. They appear almost similar in terms of features and spec sheet. Only plus point for One Plus Two is its price. The device is available at half the price of a Galaxy S6. Other than that, I do not think either of them overtake each other.

Samsung Galaxy S6 vs OnePlus Two

Display
OnePlus Two features a LTPS LCD capacitive fully HD touchscreen of 5.5 inches which sheds in beautiful color spectrum with the help of its 401 PPI pixel density. The display has 1080 X 1920 pixels resolution and it is protected by the Corning Gorilla Glass 4.

The Samsung Galaxy S6 features a super Amoled capacitive touchscreen of 5.1 inches quad HD which has 1440 X 2560 pixels resolution. It has 577 PPI pixel density which greatly sharpens the color resolutions. The display comes protected by the Corning Gorilla Glass 4.

Hardware
OnePlus 2 gets all its processing power from a powerful Qualcomm Snapdragon 801, 1.8 GHz Quadcore Cortex A53 processor which is coupled with 3, 4 GB of RAM for giving you a smoother experience. The GPU of the OnePlus Two smartphone is Adreno 430.

Whereas on the other hand, Samsung Galaxy S6 is powered by Exynos 7420, Quadcore 1.5 GHz Cortex A53/Quadcore 2.1 GHz Cortex A57 processor which is coupled with 3 GB of RAM. The GPU of this handset is Mali-T760MP8.

Memory
OnePlus 2 has an internal room of 16, 64 GB depending upon the different RAM variants. OnePlus 2 doesn't have the external microSD card slot so the users can't expand the storage space.

Whereas the Samsung Galaxy S6 comes loaded with the internal storage space of 32, 64, 128 GB and it also doesn't have the external microSD card slot for expanding the memory space.

Camera
OnePlus 2 offers a 13 MP rear camera accompanied by optical image, stabilization, dual LED flash and laser auto-focus features. Moreover, it has some more camera features which are: Geo-tagging, face detection, HDR, panorama and touch focus. On the front end, we have a 5 MP front facing camera. Both the cameras can shoot in HD quality with their amazing features.

On the other hand, Samsung Galaxy S6 has a 16 MP rear shooter which is accompanied by optical image, check quality, stabilization, LED falsh and auto-focus features. The device features some more amazing camera related features which are Geo-tagging, face detection, touch focus, auto HDR and panorama. We also have the same 5 MP front shooter in the Samsung Galaxy S6. Both the cameras can shoot in HD for you.

Battery
OnePlus 2 is fueled by a non-removable Li-Po 3300 mAh battery whereas the Samsung Galaxy S6 is powered by a non-removable battery of 2550 mAh which promises you to give a stand-by of up to 17 h (3G) and talk time of up to 49 h.

Colors & Other Features
Samsung Galaxy S6 comes in four beautiful colors which are White Pearl, Gold Platinum, Black Sapphire and Blue Topaz. The Samsung Galaxy S6 is stuffed with many sensors which are accelerometer, gyroscope, proximity, barometer, compass, heart rate and Sp02 for giving you a better user experience.

On the other hand, OnePlus 2 comes in only Sandstone Black color. The OnePlus Two comes packed with some sensors like accelerometer, compass, proximity and gyroscope. Moreover, it also features some messaging features like SMS, MMS, IM, Email and Push Email.

Verdict
Though they both are good smartphones I like OnePlus 2 among them.

Here is a detailed comparison between the two best OnePlus 2 and the Samsung Galaxy S6 smartphones. Thoug they both are very good smartphones but I will compare them to know the best in terms of design, display, processor, camera, internal storage, battery life and the gaming experience. Read the details given below to know about the best smartphone among the two mentioned above.

Build (Back)
OnePlus 2 ships with a sandstone backing which is probably a very thin layer on the top of the plastic. However, you can also get your orders in the natural and Kevlar materials if you wish to use those.

On the other hand, the Samsung Galaxy S6 backside is made up of the Gorilla Glass 4.

The design of the Galaxy S6 is also considered among one of the best designed smartphones in the list with the iPhone 6 and HTC One M9 smartphones. In terms of the design the Galaxy S6 wins with the OnePlus 2 as the Galaxy S6 has better build design. It is very thin which looks more attractive. Even it has a protective frame at the backside.

Build Frame
The frame of the OnePlus 2 is made with aluminum + magnesium metals. Whereas the Samsung Galaxy S6 frame is only build with the aluminum metal. As both the handsets are made with the metallic frames so it doesn't make much difference, they both are good.

Display Size
OnePlus 2 features a large 5.5 inches display whereas the Galaxy S6 features only a 5.1 inches display.

So here the OnePlus 2 wins as the OnePlus 2 has a bigger screen size than that of the Samsung Galaxy S6 with 16 percent (%). Though nowadays people doesn't wants to buy a large screen smartphone as it is difficult to carry from one place to another but the OnePlus 2 fits the best size that is medium, no large and no small size.

Resolutions & PPI
OnePlus 2 has a resolutions of 1920X1080 pixels whereas the Samsung Galaxy S6 has 2560X1440 pixels resolutions.

OnePlus 2 has 401 PPI pixels per inch. On the other hand, the Galaxy S6 has much greater 577 PPI pixels per inch which is quite surprised and unbelievable. Think of now you can even buy a smartphone with 577 PPI pixels per inch which will help you to view the files and folders on your smartphone even in the high sunlight areas.

So finally the Galaxy S6 wins in terms of the resolutions & PPI pixels per inch with the OnePlus 2 smartphone.

Display Type
OnePlus 2 features an IPS display whereas the Samsung Galaxy S6 outshines in a much better super Amold display.

Though the display of both the handsets are very good but the Galaxy S6 wins with the OnePlus 2 with its amazing features of the display.

Battery
Both the handset are powered by the non-removable batteries. OnePlus 2 is powered by a powerful 3,300 mAh battery whereas the Samsung Galaxy S6 is powered by the battery of 2,550 mAh.

Though both the smartphones are nicely powered by good batteries, the OnePlus 2 smartphone wins with the Galaxy S6 smartphone in the battery part.

Camera
OnePlus 2 smartphone features a 13 MP rear camera and a 5 MP front shooter. On the other hand the Samsung Galaxy S6 features a 16 MP camera at the backside and a 5 MP front camera.

The Samsung Galaxy S6's rear shooter has somehow the higher resolutions. However, that does not directly translate into the better results, but that makes it to be among the list of one of the best camera smartphones today.

Storage
OnePlus 2 comes loaded with the internal storage space of 16 GB/64 GB.

On the other hand, the Samsung Galaxy S6 smartphone has a in-built storage space of 32/64/128 GB.

In terms of storage space, the Samsung Galaxy S6 wins with the OnePlus 2 smartphone without any doubt as the Samsung Galaxy S6 have the maximum 128 GB storage space and that's really enough to store all your applications for your smartphone.

Processor & Gaming
OnePlus 2 is powered by the Snapdragon 810, 64-bit Octa-core 1.8GHz processor whereas the Samsung Galaxy S6 is powered by the Exynos 7420, 64-bit Octa-core 2.1GHz+1.5GHz processor.

You may feel free to run any HD game on such devices. Both the handsets are very good in terms of processor. Both the smartphones delivers a great smooth performance even while running any application of your wish. You can enjoy all the HD graphic Android games on these two devices without facing any lag. You can enjoy them with a smooth performance and can easily extend your Android gaming experience.

Verdict
So finally I have compared the two handsets as per key points given by you. Its really difficult to select the best one among those two as the both are really very good in every part. Though I will support the OnePlus 2 smartphone as the best among OnePlus 2 and the Samsung Galaxy S6 smartphone.

Specs comparison between Samsung Galaxy S6 and OnePlus 2 smartphones :

OS : OnePlus 2 operates on the Android v5.1 Lollipop Os whereas Galaxy S6 operates on the Android v5.0.2 Lollipop OS. The latter one is upgradable to Android v5.1.1 Lollipop OS also.

Display : OnePlus 2 sports a LTPS LCD capacitive touchscreen of 5.5 inches whose resolution is 1080 x 1920 pixels whereas Galaxy S6 has Super AMOLED capacitive touchscreen of 5.1 inches with a resolution of 1440 x 2560 pixels.

Memory :Both smartphones have 64 GB internal memory but no expandable memory. OnePlus 2 has 4 GB RAM while Galaxy S6 has 3 GB RAM.

Camera : OnePlus 2 features a 13 MP rear camera whereas Galaxy S6 has a rear camera of 16 MP. Both of them have 5 MP front camera.

Connectivity : Both OnePlus 2 and Samsung Galaxy S6 have Wi-Fi 802.11, Bluetooth v4.1, GPS/A-GPS, Hotspot and microUSB v2.0 connectivity.

Battery :OnePlus 2 and Galaxy S6 have non-removable Li-Po 3300 mAh battery and Li-Ion 2550 mAh battery respectively.