#1. i use all 3, picking up whatever class off the ground i need at the time. pretty good with all 3. I have almost all the stamps now from doing this.Its best to not limit myself to 1
#2. most of the time i run in guns blazing depending what class i am. If there is a bunch i grenade the hell out of it.If there is only a couple people i pick up a snipe from the ground as they are usually everywhere. or if there is a tank handy i drive up and unload.
#3. all of them for various reasons depending on situation