I was in your shoes a week ago. When I finally made my decision to go with the Treo, Verizon told me they were sold out in Michigan and I'd have to wait up to a week.
I had heard positive reviews about the Blackberry and decided to give it a shot and got the Curve. Love, love, LOVE it! I'm a heavy gmail/google user and the Curve syncs with google calendar beautifully. Email is a breeze and with apps for social networking like Facebook & Flickr, I now can't imagine doing without it.
Can't give an opinion about how it compares with Treo, but I'm sold on the Blackberry.