It depend what u focus on, Outdoor game? indoor game? both? All I know my brother has Aftermath Kraken but he can't bring it to Xtreme tactics because it is too fast.
But FPS isn't most important thing in game. meanwhile, Kraken is great gun for outdoor. For CQB, Look smaller guns. I see most people prefer submachine guns for CQB over assault rifle due to size advantage for CQB.
my english is bad. however, It don't make up different on your ignorance.