For powering high-drain electronics such as digital cameras, the most efficient batteries to use are 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. 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.