Grimmjow vs. Tousen
I didn't see a thread like this so I figured it was worth bringing up. Aizen stopped Grimmjow from fighting Tousen. Of course, this could be because a one-armed Grimmjow probably would have gotten himself killed and Grimmjow was instrumental in Ichigo's development.
But I digress: How would this match go in your opinion(s)? If you see this as too one sided, the fight can take place wherever you see fit and when it comes to Tousen, (i.e. SS Tousen, Hollowfied Tousen, or Whatever-the-hell-he-died as Tousen) or his abilities can be revealed the same way Kubo did back in SS and eventually FKT. Of course, the same can be said about Grimmjow (i.e. the strengths and abilities displayed during the three different times he fought Ichigo)