For mobility, I recommend a notebook or laptop.

If your primary use is browsing the internet with no gaming or the like, you may consider getting a notebook.

If you will be using the computer for more than just browsing the internet, like gaming, I strongly recommend getting a PC/tower.

If you want to be able to upgrade the computer at a later date, get a tower.

Honestly... it is all about your personal preference and what you will be doing with it.