For powering high-drain electronics such as digital cameras, the most efficient batteries to use are high-capacity Nickel Metal Hydride (NiMH) cells. Higher capacity batteries store more charge and they can power your devices longer.
The highest capacity rechargeable AA batteries are: Ansmann’s 2850 mAh batteries and Powerex’s 2700 mAh batteries. Of these two batteries, Powerex’s 2700 mAh gets the most positive reviews from photographers. It received an average of 4 out 5 stars from 98+ reviewers on Amazon.
However, in my opinion, the best choice for a high capacity AA battery is now the Eneloop Pro (aka Sanyo XX Battery Powered By Eneloop). These batteries hold their charge for 12 months. They also have a high energy capacity (2500 mAh), and they perform better than similar high-capacity AAs. See my review here.