I can't really think of a good reason not to pick up all four fighters. You've got the mobo, might as well make it worth your while.
The Hyper is a great system to pull out when friends are over. B1 is fun to play alone, too, but it's always fun to watch the "WTF?" looks change to "no, dude, you're not turning that off until I beat you, this game rocks."
I've yet to see someone not like that game, in particular, after giving it a chance.
The other three are fun, too.