If I understand correctly, you already own a 10/22 and an SKS, and can't afford to buy something else right now due to college expenses (I know that feeling!), so you're wondering which of those two is best?
My thoughts are, in that scenario, the SKS is the superior rifle on paper, BUT in an apartment I'd personally go with the 10/22, CCI Stingers, and a 25-round magazine that's been tested for reliability. .22LR out of a rifle is considerably more effective than .22 out of a pistol; out of a rifle, the Stinger has approximately the muzzle energy of a .38 Special (not stellar, but adequate), and with a 25-round magazine, it'd be a decent choice, IMHO. The 10/22 is also much cheaper to practice with (big consideration there) and you can shoot it at most indoor pistol ranges. When you're home, you could keep it chamber empty, magazine loaded, and you can unload it quickly when you're not home.
I would NOT use the quietest ammunition I could find; I would use the ammunition with the most punch. Noise is much less important than ballistics, IMHO.
The problem with 7.62x39mm in an apartment is that even with a carefully aimed shot, it will penetrate the attacker, the wall behind, and probably a couple more walls, a Very Bad Thing in an apartment setting. There aren't really any good frangible loads in 7.62x39mm, and if there were, you couldn't afford to shoot enough of them to test their reliability. I live in a brick house, so with some thought given to shot angles, I'd be comfortable using 7.62x39mm JHP's in an HD carbine (brick outer wall will stop x39), but not in an apartment.
So I'd suggest the 10/22 with Stingers, and use the money you save to get some practice time in. At apartment distances, use the front sight post to aim (don't even worry about the rear, raise your head a little so the front sight stands by itself) and practice at 5 to 7 yards on a B-21 type target. Also be sure to practice chambering the first round and flicking off the safety. If you do have to use it, shoot carefully and make each round count, and don't shoot wildly for your neighbors' sake.