Bolt action 308. My priorities for weapon use would be:
1. home defense
2. hunting - another important aspect of survival, food.
Priority of rifle attributes would be:
1. reliability
2. ammo availability
3. rate of fire
4. accuracy
5. target aquisition
6. portability
7. range
8. recoil
In a nutshell, I would be tempted towards a semi-auto for rate of fire, but I'm not sure about reliability issues. I know AR's are relatively reliable and AK's even more so, but they are gas systems with moving parts. A bolt gun will most likely work forever, no parts necessary. Keep It Simple Stupid applies here.
223, 308 and 7.62x39 are the obvious ammo choices, since they will be easiest to find ammo for. Since I've opted for the simplistic reliability of a bolt rifle, then no point in skimping on power. 308 has enough power to effectively take down men even with kevlar vests. Has plenty of range (commonly shot in 1000 yd matches). Most defensive situations will be inside 200 yards anyway. Even if I ran out of reloading components, I'd have a decent chance of finding more ammo. Recoil is not excessive. Could have a 308 bolt rifle as light as 5.5 lbs if I wanted and a short carbine barrel if I so chose. 30 cal AR's, AK's, CETME's, FN FAL's are all in the 10 lbs range. (Ruger Mini's are nice and light but again, not sure if I want to trust my life to a gas gun indefinitely) If I find myself in the mountains, running for my life, I don't want to be lugging around a 10lbs gun before I've even added a scope or ammo.
More specifically, I would want a Mcmillan Edge stock, any action (won't matter much because once they are trued up they all shoot), detachable box magazine 10 rounds, Krieger 5R 18" fluted barrel, 11" twist, Jewell trigger at 1-2lbs., Nightforce 1-4x tactical scope w/mildots. Finished weight should be in the 8lbs range including scope and mag. If bedded and trued properly and using decent handloads, should be 1/2MOA capable out to 600-800 yards with alot more man and game animal stopping power than a 223 or 7.62x39.