Interesting question!
Supers. I'm always on the lookout for my next favorite supers system. I want to play them, but if I want them to happen at all I usually have to run them.
I love superhero comics, always have, and always will, so getting to jump head first into that milieu is always a blast.
Sword & Sorcery. I love the grittiness and tone, but I have trouble getting groups to buy in; to the average fantasy gamer it feels like a D&D game with fewer options.
Low fantasy. I like relying more on character and skill than on magic and other superpowers, but this shares a similar problem with S&S, above.
Hard scifi. Again, less about characters with superpowers and more about characters dealing with challenges in a more naturalistic albeit high-tech society or environment. Systems for this seem to be few and far between, but is love to stand corrected!