First off, if you’re interested in raw numbers, you can check out this numerical MU chart compiled by @Phrawger:
It combines MU scores from several notable players’ own charts to try and gauge a sort of consensus average. You can also page through and look at each individual chart as well.
As for your actual question, I’m not sure which ones I would definitively say are “most balanced.” Otherwise, I would generally say that any MU that isn’t one of the high-profile lopsided MUs (
v 
, 
v 
, 
v 
, etc.) is close-enough to balanced as to be a non-issue.
If pressed to give a specific answer, I think that 
versus is close to even and very fun to play, provided the player knows what they are doing.
Of course, none of that changes the reality of the carousel. If that’s ultimately your worry, your choices are:
- Give in and play the carousel.
- Play a non-carousel character and make up for it in player skill.
- Sign up for @mysticjuicer’s 19XX tournaments.
Anyways, maybe someone else can do a better job than I of outlining the most balanced MUs 
.