I first bout the Duratrax 4200's for my E-Maxx and use them in my Slash. They are a good battery. If you don't want to go Lipo, the best NimH I have found are Spec Point Concepts (http://spcracing.com
). They are pricey, but have a lot of punch and good run times.
A lot of good points about Lipo for the long haul though, I am still just nervous and have two Duratrax Piranha's that I don't want to part with yet.