I went with the 2720. It was a bit of a tough call. The 2610 is highly regarded and they dropped some niceties in the user interface when they designed the 27xx series. On the other hand, the 27xx series has a higher resolution screen that should be more viewable in sunlight. (I figured since I hadn't already owned the 2610 I wouldn't miss things like transparent display.)
It seems like the 2610 would have required a 2GB CF card to hold the maps that come installed on the 2720. That means I'm comparing the 2610 at about $600 ($499 + about $100 for the CF card) to the 2720 at about $750.