I think only you will be able to make that decision after viewing both phones in person. I just bought the Droid on Friday evening and more I use it the more I love it. I came from Tmobile and a Blackberry.
When I first saw it in person (after doing so much r esearch on line and on youtube) what struck me most was that it was not as large as I was expecting. I certainly wanted a large phone, but I was expecting a brick for some reason. It's a nice size, and still fits nicely in my shirt pocket. It's a handsome phone, definately masculine (I do wonder how females like it). Everybodys mileage will vary with the keyboard. I personally like the option. Most work so far i've done has been in portrait mode so obviously I am using tre portait virtual keyboard. Surprisingly in two days I am becoming faster. I am not a small guy either.
I also viewed the Eris as well and was struck at its clean smootth lines and the rubberized back. Did not seem cheap in any capacity. It''s a nice looking phone as well, smaller than the Droid and has a nice feel. I sort of wish the Eris' lines and feel were incorporated into the Droids size. But I like the Droid as it's a very strong piece of hardware. Looks great and is power in the making.