You can't really compare how one weapon (or class of weapons) would fare against another weapon head-to-head because you're going to play differently depending on the map (and even your style of play).
That said, I think there are some weapons that are a little easier for more inexperienced players to develop their fundamentals on before discovering their own game play style (or these are weapons that made it easier for me to go from total noob to almost average).
Quickdraw and Stalker
SCAR-L (use the M4A1 before you level up to the SCAR-L)
Fairly clear iron sight so you can save an attachment for something else and not worry about being EMP'ed, fire rate isn't as fast as other AR and it's got a smaller magazine, but it's got power and it'll teach you to pick your shots and not spray like nuts.
Sub Machine Guns:
Very clear iron sight, fire rate isn't as fast as other SMG's, but it's accurate.
Light Machine Guns:
MG36 (use the L86 LSW before you level up to the MG36)
IMHO, the MG36 feels like an assault rifle, but still has same punch as an LMG.