Here's my current top 5 (actually 6)
5) Morrow Project
4) Twilight 2000
2) Gamma World
0) Darwin's World (I'm ranking DW 0 which means it's the best or worst, you decide)
5) Morrow Project - I've never played this one, but it's been around a long time and has a good following.
4) Twilight 2000 - again, never actually play this one but have the rule books. It's a classic and lives on in 2013.
3) Aftermath - this one is the quintessential PA RPG. Very mad max and is a great baseline for any pa setting. Kind of lives in Gamma World's shadow and probably doesn't get enough credit.
2) Gamma World - yeah, I know most people would make this 1, but it's never really enjoyed great commercial success. It's a legend and has a special place in the hearts of every PA fan. It's so uncanny how much it is still beloved since it's been so mistreated by publishers. It's like a good mutant; it keeps evolving and refused to die despite constant hardships. I hope someday someone gives this property its due. If only I had the money to buy it.
1) Rifts - probably a controversial #1. Yeah the system is broken and completely unbalanced, but it's commercial success and appeal is undeniable (what is there like 100 books by now?). It's one of the most unique PA settings ever created and probably the most fleshed out. Like Gamma World, I wish I owned it and could do a new edition.
Anyhow, I want to know everyone's top 5 and include DW where you think it should be (even if not on the list). Also, if you can add to this complete list below, please let me know any pa games I'm missing.
After The Bomb
Daemornia: The Role Playing Game
Deadlands: Hell on Earth
Exodus Survivors Guide - former fallout rpg