I've looked at both of em, and I know I'm getting the droid. It may be more expensive, but atleast in my opinion I like how the Droid is more orientated towards "techy" people, and isnt so "dumbed" down as the Eris in it's menus. Again, IMO, its like Window's Vista, its almost too user friendly to the point where it seems to compromise the phone's general functionality. Also, keep in mind it is a Windows Mobile phone, NOT an android phone, so you have a pretty low quality OS to deal with compared to Android 2.0. Seems like a re-release of the imagio on the most part for me.
Hope it helps! Just my opinion...