A great thread can be found here:
http://forum.ppcgeeks.com/showthread.php?t=46616
As with most of the stuff on this site, though, try it out and find out for yourself. I have sprint, and most on that thread recommend the Altell radio, however where I am in South Carolina the internet seems to bug out a bit more with that radio version. I have tried four, and found my best results (battery life & connectivity) to occur with the Sprint 1.11F.
Again tho, these are my personal results. Try them all out (can't really hurt anything as it won't hard-reset your phone), and find what works best for you.
A