My wife had a Storm 1 and at first she was very pleased with it...her (our) first Blackberry, heck it was her first "smart" phone. Soon, though, its shortcomings started creeping up. The corners of the screen didn't click well, and the lack of memory was a major problem. She would have to do a battery pull just about every day (as do most storm owners). Well, about a month ago it finally died on her, completely. We went and looked at the Storm 2. While it does improve on some things over the Storm 1, it was still the same ol' Storm. I then urged her to look at the Eris. She fought me on it (she doesn't like change), but after playing around with it for a while in the store she decided to get it.
She couldn't be happier. Don't get me wrong, it does have its cons....battery life, no BBIM, etc. But overall she feels she definitely picked the better phone. She loves the 7 screens HTC has with the Sense UI and the various widgets you can put on them. The OS is just much slicker than the Blackberry.
Sorry for being long-winded....for what it's worth, my suggestion would be that if you like your Storm and don't have any problems with it, maybe stay with it. But, if you do have problems with it or are annoyed with the shortcomings (memory), I'd definitely recommend the Eris. I think you'd like it a lot. Or, if you can wait a few months, the Passion/Bravo/whatever will be making its way to Verizon...that may be worth the wait.
Good luck!