They aren’t that different for cameras with similar functionality. i tend to look mostly at the Canon digital camera models, as they have the most diversersity. They also often seem to often offer better value than Nikon, although for those who already have Nikon lenses, choosing a Canon camera usually doesn’t make sense(the lenses aren’t compatible). While neither Canon or Nikon makes a digital SLR that uses AA batteries, Pentax does make some of them. Notice though that there are optional battery grips for Canon and Nikon SLRs that will allow the cameras to be powered by AA batteries.
Removing a battery to charge it is a positive factor, not a negative one. The heat generated when charging a battery adds extra wear to electronic circuits, and shortens their lifespan. I guess charging a battery internally is desired though if someone wants to design something that is disposable.
