I have a 700P, Palm OS as opposed to Windows, the w\wx. Wife had a 6700. (Hated it).
For me, the 700P cannot be beat. It is probably the single best PDA\Phone I have owned. The fact that I hate windows mobile, or windows in general, is probably one of the reasons, but the Treo is just a great device. For a combo, it's got a great form factor, has been very reliable, and has better phone reception than even dedicated phones I have had. Couple that with all the features and stability of the Palm OS, and I don't think you can go wrong.
I'm also with Sprint, and have been for over 5 years. I don't think I"ve ever dropped a call, and there data plans are simply amazingly affordable. I'm grandfathered, but basically I pay $15 bucks a month for unlmited data, which is now EVDO speed with the 700P. Yeah, watching streaming video is kinda cool, LOL.
Anyway, I vote for the Treo. Great device.