I prefer the P90 for my stealth class it works much better.
I agree, the P90 is much more efficient at killing. However, I do not like the sight on it, so I usually go with Red Dot + Silencer using Bling Pro. It works well, but It usually ends up with me having to use my PP2000+RDS+Silencer when I run out of ammo.
I like the Uzi's sight however, so I usually go with just scavenger + Silencer. It leaves my secondary weapon slot open for something else.