To be honest I can't say that I have a "favorite" yet because I don't think any of them come close to my idea of perfect. I've probably put the most time into Wasteland/Fallout so if I had to pick that would probably be it.
My favorite post-apocolypse settings tend to mostly be vintage RPG ones. Gamma World, Metamorphisis Alpha, Morrow Project (to an extent), and others with varying degrees of seriousness.
As cool as the idea is, as someone who is pretty much unfit to survive the collapse of civilization I'm not as into the idea as I once was. I'm a realist, when I was in better shape, and quite dangerous, the idea was sort of appealing on a primal level. All these retarded fat cat pencil pushers who haven't ever been in a situation where they had the slightest potential for danger, or done any real work either dead or having to deal with me, the mere security grunt in a situation where I'd be holding the cards (to so speak) not that I'd be brutal or anything, it's just that as far as the fantasy goes (and to be fair that's what it is) I could almost see it as a possibility.
The thing is that I am increasingly fatter and sicker, heavily medicated, and have brain damage that seems to be slowly having worse effects. I function as well as I do now largely because of the support of civilization to get medication, and an infrastructure that has made my family well off enough where I can get by living at home for the time, though when that situation changes, it's going to be touchy, and a lot depends on what's left of me.
Kind of depressing to say (though I've said it before), and the point it's to go Emo here, it's mostly just to point out that while I play post apocolyptic games, it's hard for me to really get into the "fun" of the fantasy they entail at times, because there isn't even the slight sssociation of "maybe I could survive" because I know I wouldn't. There was a time I could have done some of that action adventure stuff in the right circumstances (though it wouldn't like the movie version, it rarely is), now, not really. I can barely get my to or above my waist anymore, and can actually feel the fat on me jiggle (which is pretty bloody disturbing).