I used NiCd/NiMH AA for quite a while, but they're a pain in the butt because if you aren't constantly exercising them, you'll forget that they drain just sitting in the drawer, so you miss charging them up the night before something important, and when you get to where you're going, they're practically dead already.
So then I switched to just regular old alkaline, but apparently sticking them in the fridge doesn't work anymore, or maybe I didn't let them thaw out enough. I dunno... supposedly doing that keeps them fresher longer, but it didn't work out that way at last year's Doodah parade, and I was rather pissed.
The next set of AA or AAA batteries I buy are going to be those Energizer lithium jobs. I've never had a single problem with the lithium packs in my cell phone or the Canon I got from Haze's buddy, so I figure I might as well give them a try in my calculator (which eats AAA's like candy) or my wireless PS2 controller and see how they do.