Assault rifle with SMG secondary, possibly Mossington.
I don't really know anything about guns (or really care that much for them) to distinguish between any of them, but I usually play with assault rifles and SMG's a lot in most video games. I'm not a shotgun kind of person, since I like to reload and shoot fast.
Likewise (on both) - but I do find that it varies considerably from game to game - i.e. it will depend a lot on the actual balance of assault rifles in Brink as opposed to assault rifles in any other game. For example, I prefer dual pistols in the Left 4 Dead games.
I'm pretty certain assault rifles and SMGs will be my weapons of choice, though.