PP-19 in any variety is lotto head shot king! Plus you'll have the highest magazine count at 65 vs the P90 at 50. Off the top of my head I'm certain it's more accurate and deals more damage as well. But you're comparing apples to oranges with the:
and here's why:
pp19 camo ....mod..
The Scar class weapons are assault rifles. The P90 and Uzi are sub-par at best for midrange firefights. The PP-19 will win a few midrange fights. The Scar will win all of the midrange fights against those SMG's and certainly the longer firefights.
So what are you looking for? If it's an assault rifle with great accuracy, low recoil that doesn't rock side to side, and decent damage then I suggest the M416. There's no need to buy the M416 CQB. It's far too weak. It's the same thing as putting a reflexive scope on the M416 except the GP M416 is stronger. The SG550 is a good weapon but also underpowered. It too recoils on a Y axis so you'll get plenty of lotto head shots if you aim for the chest and squeeze.