Scarecrow,
How much ammo with the AR-10?
Since it would be used primarily as a defensive weapon (no need to waste ammo), I would probably go with number 1. The large quantity of ammo you could carry, plus the great capacity of the C-mag (100rnds.), would put this weapon in a similar tactical class as a SAW (though NOT fully automatic, lighter barrel heats up quicker, etc.). It would allow you to manipulate your weapon less during combat.
Number 2 is a bolt gun, and I would take it only if given no other option, due to the fact that combat conditions would be such that it would only be useful in a sniper/countershiper role, as it is accurate and has the best penetrative capabilities of the three choices. However, the slower operation of the bolt and limited capacity would not be suitable for an all-around rifle.
Number 3 and number 1 are almost tied in my book for the one weapon I would take, because you may need to shoot through semi-hard cover (auto bodies, etc.) to neutralize the threat, and it is also a semi-auto. However, I don't know how much ammo you are giving in this gun in this sit. Assuming all you had was (fully loaded) two 20's, one 5, and three 30's (40+5+90=135 rnds.), I would RATHER have choice number one, simply for the extra ammo. Also, if you are going to be fighting your way out of a metropolitan area, the longer weapon may be a little more of a hinderance in house-to-house "alley" combat (ie: how you would probably move to avoid being in the open and if all roads were blocked up). Also, weight of the rifle is probably more, and the heavier your weapon is, the more likely you will put it down when you NEED it suddenly.
BTW, I wouldn't have the Glock 17, nor the 30 rnd. mags. I would rather go Beretta, but that is a personal preference (Glock doesn't fit my hand well). I would stick to 15 rnd. (17 for you) mags, because it makes it easier to carry, since it is your secondary weapon, not your primary.
My .02, take it or leave it,
Urban
[sniper]