My survival rifle would be a sporterized Mauser in 8MM. Why?
It's the only rifle I currently own!
I suppose it depends on what "survival" entails. Is it just having to hunt my own food for three months while waiting for rescue, because in that case a bolt-action .22LR makes the most sense to me, but if it's hunting AND maybe people are trying to kill me (SHTF), well:
As far as hunting goes I would probably use trapwire and my laminated re-curve bow (not necessarily in conjunction), since I can craft an infinite number of arrows given the proliferation of trees in the woods, I can always make more arrows, even reloading eventually your cases will be trashed. Plus arrows are powerful enough to kill Deer sized game, but can also kill a rabbit without obliterating all the meat.
For defending against people, something semi-auto, in a decent caliber, and easy to maintain. I'm not super psyched about it, but I think an AK fills that roll quite nicely as far as rifles go. They aren't as ergonomic as an AR, but they will keep on shooting, even in the hands of someone who is 100% clueless on how to maintain them (I am only 90% clueless on how to maintain an AK). Don't get me wrong, I don't own, and probably will never feel the need to buy, an AK, I just think it fits the role well, since I'll be hunting with my bow anyway.
Though if it didn't have to be a rifle, I would probably choose a 12GA shotgun to go along with my bow instead.