I would prefer characters and costumes, and would be willing to get stages if they are interesting enough and cheap, or bundled together.
Ideal scenario for me:
$5/ individual character
$1/ individual costume
Bundle them in a Season Pass for a cheaper price...
6 characters = $20
8 costumes for $5
I would be satisfied with that. I'm not wanting to spend an extra $50 on DLC. $20-$30 is acceptable, if it means another 6-8 characters, and another 6-8 attires.