You should get the phone that fits your needs. When I first started looking at phones, I didn't particularly care for the Moto Droid because of it's weight and size. Performance wasn't even really a concern. When I did finally purchased my Eris, I loved it and it worked great. So much so that I didn't jump on the 2.1 leaks nor root when it came out.
Once I finally did root, it kinda set off my tinkering mentality. Only then did I regret getting the Eris in the slightest. Even now, the only thing I regret with the Eris over the D1 is the amount of modding that is possible on a D1.
The Eris gets a lot of flack for being slow and "unusable," but a lot of it comes down to what you want from your phone. Most people aren't power users like nearly everyone on the forums here and the Eris works fine for them which is why you still see the Droid Eris selling for about $175-$225 on Craigslist and the Moto Droid going for $200-$250.
...And I'm rambling on about nothing again, haha. I have a habit of doing this anymore.