Started with an 8830 World Edition and moved to 8330 Curve. Now on a Storm. Ease of use - Curve. Flexibility - Storm. Future? VZW Niagara maybe. First PDA phone - Palm Treo 700w.
I've gone through a 7105, an 8700, and my current 8320. My favorite was the 8700; it just felt really solid in my hand, the keyboard is better than my 8320, and I prefer the click-wheel to the trackball.
That said, I wouldn't willingly trade down because I like the expanded functionality of the Curve: the camera, the MicroSD slot, etc.