Man o man what a diversified bunch of answers!
It depends on what cell type your batteries are! Huge difference!
Nicads can be charged super fast, personally I wouldn't go over 1c if you want them to last a long time. Yes you can go faster but the charge and life will be decreased. Super fast chargers are for electrics that are using the batteries for motors and such, not receiver packs.
NiMh I would only go 1/2c absolute max, and make sure your charger does NiMh properly.
If their NiMh's just charge them more often, they have no memory effect like NiCads do so you don't have to fully cycle them.
Good Nimh reading here, and if you go back to the home page he addresses Nicads as well
[link=http://members.aol.com/davthacker/nimhfaq.htm]Nimh battery FAQ's[/link]