I will vote for both, sometimes you require a internet facility while travelling in road transport. you may require a to send a important mail or some important information, either you can call somebody to do the work, otherwise you need to need to go home or office or browsing center to use the internet.
Laptop and desktop cannot be used in all the places, or at least wherever you are travelling.
If you are in home then everyone prefer to use the internet in laptop or desktop, because the screen of the mobile is so small and speed will be low compared to your laptop or desktop
Mobile internet will be helpful when you want to the updates of cricket score or football score or some important updates you require a mobile internet
Both will be useful based on your usage or need and it depends on your work. If you are in support project then you may require a internet mobile so that you can receive a mail or you sent mail
It absolutely depends on your necessity.