SCAR. Accurate as can be, slow yet easy-to-control fire rate, little recoil, and overall awesome looking.
As an added bonus, it's made by the guys who made the P90 for the US Special Forces (as a replacement for the M4A1). Automatic Kalashnikov 1947s have a heck of a lot of power and are pretty nice, and the German G36E has a nice state base with a built in scope, but such things come at a great cost. The SCAR is straight forward, good for tuning up or just for bringing onto the field. Suggest a scope though, and suppressors are ok. Just don't put on that extended magazine crap, it's just stupid to promote spray and pray. Once you get along pretty well with the fire rate and CQB, try upgrading to the M14 and a red dot. I'm a spotter providing my sniper with close-mid range support, and it works pretty darn well with a lot of power in each bullet (STILL NO EXTENEDED MAGS!!!). OK, I'm done ranting.