The 8703 is a solid device, but if you have the option I'd recommend the 8830. Make sure you get the new $30 Blackberry (BIS) plan if you can, too, if you don't already have it.
I very much prefer the trackball devices over the trackwheel any day. Much easier to navigate, and the trackball eliminates a lot of steps (simply clicking on an email opens it with the trackball vs. having to click the wheel or press the Enter key).
Plus you'll be able to get a microSD card and put pictures, music, ringtones, on the device (4GB is the largest size supported for that device/OS).
My 2 cents