DoubleSb

It's mostly preferences and then budget. I got an M4 because I like them. I wouldn't reccomend a sniper rifle unless you are going to be playing with a BUNCH of people because otherwise everyone will just avoid you or go after you.

Depends on your play style, I would recommend an assault rifle though, M4, G36c, MP5, M14, AK-47/AK-74/AK-74u. AUG, STG 77 (I think it has a new name now), Scar are popular ones.

If you are looking for good brands, I wouldn't go cheaper than JG or ECHO 1, unless the price is a steal. Make sure the FPS goes to at least 300 too.

Try to get one with a full battery and not a small stick one.