My wife has the Droid and I have the Eris, so I've spent time with both phones.

The Droid is an Iphone killer. Primarily because of the giant display.

The Eris is an Iphone alternative. The first one from Verizon. It's as close to the Iphone as Verizon has gotten.

I chose the Eris because of its size and weight and because of its more polished interface.