March Madness OSR Challenge Day 11

What post-apocalyptic RPG have you enjoyed most? Hmm...I'll go with Rifts.  But this is a hard one, since I like Gamma World--in particular the most recent addition based on DnD 4E, Mutant Future, Omega World, and Waste World.

Why?  It's gonzo, it takes everything, the kitchen sink and Atlantis and throws it all at you.  It's the epitome of what Cross Planes means to me.  A dragon, a 'borg, a cowboy, a ninja, and a Dog Boy go into a bar--it's no joke, that's how the first session starts!