Blazblue is awesome (granted a little meh at it now that they changed Hazama and haven't mastered his new consoles + dashing sucks using the analog stick on 360 controller)
Pfft. Hazama is way better now that he has more than one combo.
And let's see... can't help on Tekken or SC, since I never really cared for them. MK9 is pretty fun and it has a solid engine, but it's not my cup of tea, so I guess I can talk about the other ones.
BB is finally good in CS2. The good news is, you can probably find CS pretty cheap now and the update patch is free (I think). You'll still need to pay for the 3 DLC characters if you want them, and that runs you about... $20? $15? Not sure how they're priced.
BB is, I think, harder to just pick up and play at a casual level than the Capcom fighters. People exaggerate when they say you need to know 30+ combos to be good, but it still ain't easy.
SSF4AE you can get for $40 and it's pretty good. It's a little slower than the other games in terms of how it plays, but rounds go by a lot faster than BB. You have a lot of character diversity (even if the game is kind of unbalanced right now), but a free balancing patch is on the way.
AE is probably the easiest of the games to pick up and play on a casual level, but you might find that how link-reliant some characters are can be worse than the long combos of BB.
Marvel... I'd say just wait for UMvC3. Game can be fun now, but it'll be obsolete in a few months. Probably either a little harder or easier to play than BB on a casual level.
My verdict: Be a cool dude and pick up KoF13 in October.
--
"Oh God, maplejet's trying to be cool again. I'll call the ambulance." - Wylvane