http://bf3blog.com/battlefield-3-classes/
I have less than an hour played and I can already tell you that it is frustrating as hell trying to figure out what class I want to play. They are all so different in ways but then you can use unlock able weapons for every class. Classes have specific weapons but there are different weapons that unlock as you rank up.
The reason for taking so much time in choosing is you don't unlock any class specific items unless you play that class.
~jkbucksot