PS1 has been my main focus on collecting for a while, but now that I'm close to done with that, Saturn, Dreamcast, Genesis, 3DO and Jaguar are my current favorites to collect for, and I've been slowly finding boxes for my nes and snes loose carts. Just got a box for super turrican and super mario world the other day!
I also got a Game Gear recently and it's been fun checking out games for that, never had one as a kid.