I checked out both and initial like is the Eris. The feel of it works for me. I have the Dare, so close in shape and feel, but it ends there. The Eris has the 7 home screens which I like. Light is a + since I keep it in a pouch on my belt. The pinch/zoom feature is cool as well. Do not really need a physical keyboard.
Things I do on my Dare:
check email(google and yahoo) do not care for exchange or pop3
read the news(CNN, Foxnews, etc)
Youtube - watch videos
Facebook/Myspace - keep up with the status and replies.
take Pictures/Video - not a lot, but enough
GPS - Yes, I am paying for it right now.
Games - not really
Text - I like the virtual keyboard over my wife's LG touch physical keyboard.
If the Eris will do the above, then I am set. Yes, it will have an upgrade, but when is the word. If attachments can be read, then I will use this feature as well.(pdf, word)
I know the Droid will do a lot more, but do I really need it? Not sure, still shopping and reading the forums.