I really can't see the comparison of Mobile and a PC/Laptop

, mobile is a completely different issue and is very usefull anywhere you go. And provided a laptop is also a computer. So I'd take it as desktop or a laptop.
However when it comes to a desktop or a laptop, it really depends on what your need is. If you work in an office and you have a need computer with you all the time, you go for laptop. But if you dont need a computer much then take a desktop as desktops are way costlier than a laptop.
PS - Desktops are larger than a laptop
