Kel-Tec's Sub-2000 would be nice, since I'm planning on getting a Glock 19. I'm on the outskirts of town, though, and there's a lot of farmland in the area. So, a .223 would be a much better choice, considering I'd actually have a chance of taking down deer with it at reasonable ranges (in a survival scenario, of course), and could function acceptably in a firefight.
I'm not really concerned about scope mounting, because I plan on only using irons - not just because of weight, but also durability. If the gun has a detachable magazine, it's a major plus if I can use AR mags, and the availability of spare parts is definitely a major consideration.
Yes, the SU-16 is a bit lighter and shorter than the 180 (or at least the C model is). The latter, however, uses standard AR trigger group parts, which is making it look a little better for my purposes at the moment.