Well, to tell you the truth, their about the same. If you have the money, get the Motorola Droid, I enjoyed both phones, however I liked the Motorola Droid better.
The problem with the Eris is that it's running Android Donut (unless they updated recently), while the Motorola Droid is running Android Eclair, because of this the Motorola Droid has less failures IN GENERAL. Every phone you get will have a glitch somewhere along the line, however, I think the Motorola Droid had less failures overall. If they updated the Eris, it doesn't matter which phone you get, however the Motorola Droid has more processing power, so things will load faster. Remember, no matter how good of a connection you have, the phone can only go as fast as it's processor can go.