Probably partially depends on the axle you are using, but certainly on usage.
Easiest/most available/best reputation is probably an eaton. Not the gov-lock lol.
Zexel Torsens have a good reputation too, but I'm not sure all what they are available for. May only be 7.5" rears.
I'd shy away from a locker if you plan on running it hard in corners. The lock/unlock characteristics wouldn't really be worth it for a vehicle that never needs the actual locking characteristics of them IMO.
8.5's get a pretty bad rep in trucks, but in actuality they can hold up. Plenty of cars run dang fast in the 1/4 mile with no breakage. Not to mention all of the new trucks putting down how much power and running 8.5's? As long as it wasn't a gov-lock, I don't think I'd cry over a 10 bolt. Besides, posi 8.5" carriers are pretty easily found in Caprices and other big cars. Not all big cars got the 8.5" (7.5" was essentially standard) but they are out there. Would be a cheap way to "test" if you like the posi and have a 10 bolt already.