ohhh, another confession, I'm an ex R/C Car geek, (>batteries = win races) basically, Nicads are old hat, NiMH are okay as long as you buy some with a big a number as possible ( >2000, the higher you go the more money you pay). Basically, think of the numbers on the batteries as 'how much capacity they've got). that's it, hope this helps. rechargeable battery packs are great as long as they keep getting produced.... AA's will be produced for a while yet.... and it's the same hardware in essence, greater maH rating = more longevity.
Don't write off using AA rechargeables necessarily - You can always run a digital camera off duracels in an emergency - but you can't just pick up a specific rechargeable battery when you forget to pack the extra one you need when your main one has discharged.