Day 17: Favorite Fantasy RPG
Dungeon World. This is the D&D-style adaptation of the Apocalypse World engine. Just so accessible and easy to run.
Day 18: Favorite SF RPG
Star Frontiers. Only cause it's the only one I've ever really run or played back in the day. I haven't played Traveller, or The Last Parsec, or others, so can't compare. I know that Star Frontiers as an original system sucks, but I just loved the setting (in all its somewhat pulpy glory). And because of the Savage Worlds conversion, you don't have to worry about fiddly early 80's d% mechanics and tables.
Day 19: Favorite Supers RPG
No opinion. I just haven't played much or any supers. Big gap in my gaming background. Fate is the closest I've come to this, and specifically a game of Atomic Robo, and it seems to work pretty great for it.
Day 20: Favorite Horror RPG
Dread. I love me some Cthulhu, but have just played so many good Dread games, and it really lends itself to some awesome PvP action in a way that works really well, since really, someone's gonna have to drop.