Now, before I continue, just remember. This is my personal opinion. If Ты disagree, that's fine. Just Показать some respect for it, and I'll respect yours.
If Ты ask me, I think a crossover game/anime/manga/comic book between Rosario + Vampire and улица, уличный Fighter would be awesome. I could picture these rivalries easily:
Ryu Vs. Moka
Ken Vs. Tsukune
Dan Vs. Kurumu (Allure Vs. Super Taunt)
Q Vs. Mizore
Sagat Vs. Kokoa
Inner Moka Vs. Evil Ryu
What about Ты guys? What rivalries would Ты think would be good?