Whatever you use, don't use PowerGenix. Yes they have fantastic recycling times and are 1.6v but they are only good for a few re-charges. One out of the 4 will poop out and you will get poor recycling. When you pull them out, the one that's hotter than the rest is the bad one. I've bought a bunch from Big Lots when they were dumped around xmas. Bought about 10 sets for 4 and most of them are junk now.
I use Imedion and they are really good. Recylcing times aren't that much different from PowerGenix.
Newegg.com - POWEREX MH-4AAI-BH 2400mAh 4-pack AA IMEDION Pre-Charged and Ready-to-use Rechargeable Batteries
Eventhough you don't want powerpacks, I started using Quantum Turbos on my speedlights and they are pretty awesome.
No need to keep track of all those batteries and you shoot for hours on end without worrying about the batteries.
Just found out about Godox PB820 powerpacks. LightenUpandShoot.com guys use them.
Wondering how well they compare to the Quantums. They seem to use the same cables.