It's hard to say, really ... I like so many of them.
Blazing Star for sure, but it's fuzzier after that.
I'd say probably MOTW, Puzzle Bobble (2, if I could find it), and either KOF97 or KOF2003 for the other three.
If I could get another 2 slots in there, I'd add Fatal Fury and either World Heroes or Art of Fighting (all the originals) for nostalgia ... or maybe all 3 of those with Metal Slug X in another 4-slot altogether.
But then again, that's the beauty of having swappable carts ... I can be as indecisive as I want! :chimp: