What's wrong with the Tactical? Considering it's construction you really couldn't slim it down much, so it's a no go on subtle, but that's pretty much ARs general. It's gotta be my favorite AR in the game though, expensive as hell though. (and it's one of like a handfull of guns in the book with a non stupid picture...)
Try the P-93, which is an SMG, but it's my go to gun for almost no recoil, and good baseline upgrades. Or the HK-227 Arctic, again, SMG but the standards on it are top notch. Then there is the Onotari Room Sweeper, not a bad gun. And most of the AKs are fine and I think are only restricted.