i'm not an expert, but i'll play one on this post. from what i've read on candlepower fourms, the NIMH have a flat power discharge curve, IOW they work till they don't. that's an oversimplifaction but the good part is you can use them again (obviously) they drain off even when not being used.
for long term, non continuous use lithium batts. are the best, but with surefires, digital cameras, other power hungry flashlights they don't last that long (1-2 hrs. at best, depending on the brightness of the light) and you have to work to find them cheap.
I guess it just depends on what your using them for. we just had twins, and all their toys have rechargeables; otherwise i would'nt even have this computer left.
look on the candlepower fourms to go blind reading stuff about batteries & other light emitting toys.