Here is the detailed comparison of both these smartphones, have a look.
Design & Display
Motorola Moto G ( 3rd Gen ) comes with 155 grams of weight and with 11.6mm thickness. With IPS LCD Screen and of a screen size of 5 inches of 720 P resolution is a quite low considering there are many mobiles in this range offering full HD ( 1080p) and pixel density is also not so good with 294 PPI with Corning Gorilla glass 3 protection.
Lenovo Vibe S1 measures 132 grams of weight and with 7.8mm thickness. This also features IPS LCD screen with a screen size of 5.0 inches and with a Resolution of 1080p and of a pixel density of 441 ppi. Corning Gorilla Glass 3 protection will make it safe for long use.
Software & Hardware
Motorola is powered by Qualcomm snapdragon 410 and with a Quad-core 1.4 GHz processor with the Android OS, v5.1.1 (Lollipop) and it is upgraded to MarshMallow.
Lenovo Vide is comprised of Mediatek chipset and with Octa-core 1.7 GHz will make sure you run your graphics smooth and with the Android version Lollipop running on it and there is no news on MarshMallow update.
Camera & Memory
Motorola has 13 MP Rear camera and a front cam of 5MP ( auto-HDR ) featuring autofocus, dual-LED (dual tone) flash options for the rear camera.Videos will have support to record at 1080p@30fps, HDR. This is available in 2 options of 8 GB, 1 GB RAM and 16 GB, 2 GB RAM. Also has support for internal storage with support up to 32 GB.
Whereas Lenovo is with 13 MP rear camera with support to phase detection autofocus, dual-LED flash which will help you to take pictures even in low light and with a front camera of 8 MP is a great one ( Once check the quality of sample pictures, these day brands are concentrating on numbers and providing poor quality lens with bigger MP ). With 32 GB, 3 GB RAM and also has support to memory card up to 128GB.
Battery & Price
Motorola with a Non-removable Li-Ion 2470 mAh battery and is available with a price tag of Rs 12,999 in Flipkart.
Lenovo with a Non-removable Li-Po 2420 mAh battery and its available in Amazon with a price of Rs 15,999.
Even though Lenovo has attracting feature and far better when compared to Motorola but Lenovo has the lack of consistency in the long run. so once check with the review of someone who is already using that and if everything is fine, go with it.
If long lasting performance is your concern, go with Motorola Moto G3.