Manual. For a street car that sees the 1/4 a few times I say you can't beat the fun factor of a manual. AOD's can be fun when built, but damn, by the time you get a stall, heat exchanger and line upgrade, one piece billet input shaft, internal upgrades, valve body, etc... you are broke. And you never know exactly where your stall will be...you just kinda hope for the best.
Manual, you just get a good clutch. Done. Everthing else is good to go unless you prefer a tighter shifter or something. But interals don't really fail anymore than an AOD. Mine have been fine for 4 years now....and most internals that fail, were going to fail anyway regardless of power.
Wheelhop doesn't really exist for me anymore. First gear rips so quick that you just spin. And it's a blast to drive on the slicks. No doubt my manual tranny is leaving some e.t. on the table....but I don't think it's that much. If i swapped to a C4 or AOD, my 383 RWHP would become something like 350 RWHP or less. And I would be very suprised if the car could bust into the 11's. SO what's that...4 tenths improvement? I'll keep the manual (for now).
P.S. M5R2 will technically be "supported" for quite a while. Several companies keep good used parts on hand to keep you running. The problem is these trannies shift like such horse$h!+ that BRAND NEW parts vs. good used parts is the difference between "acceptable" shifting and "poor" shifting. Which is only noticing mainly when racing. So if you aren't racing the car alot and need parts to keep enjoying it....you'll be able to keep servicing that M5R2. If you want peak performance out of it....thats a different story.