Unless you're beefing up for a future HP/TQ upgrade, I'd recommend rebuilding what you've got and maybe get a hardened set of 28 spline axles. Your 8.8 will most likely outlast several T5s. I plan on reclutching my 8.8 as many times as necessary until it blows up. Once I start tearing it up, then I'll invest in something different. Probably a spool by then.
Here's another recent post relative to this topic. Maybe you'll find some useful info there:
http://forums.mustangworks.com/showt...threadid=28050
However, if you're set on upgrading from stock, I'd recommend an Eaton or one of similar design. Something you can rebuild in your garage when the time comes. Even the good ones will where out eventually.