Which Smartphone Should I Get From AT&T?

I am availible for an upgrade this weekend. I have been doing alot of research on phones and decided to go to a smartphone. I will not use it alot for email, but for an all around affordable phone that is worth 18 months till my next upgrade. I am stuck between the Treo 680, ATT 8525, & the Blackjack. Any support would be appreciated...Thanks Alot.