When I use SMG, I don't usually use supressor because the magazine is really small and with a faster rate of fire, those bullets run out pretty quickly. So consider using Warlord Pro as your 2nd tier perk so that you can attach a supressor and extended mags to your SMG.
Now to your main question. I am a big fan of the PM63. It's not accurate in long range though, so you'll have to plan accordingly. But it's pretty strong at close range with its fast firing rate. The other SMG I like is the MP5K which has a slower firing rate but the bullets do more damage.