i actually don't like DUO's in comparison to the PB1xx series. their keyboards are horrible and the trackball, while truly awesome and cute, is actually not nearly as nice to use.

i would recommend pretty much any of the active-matrix greyscale models, i personally own a 160, 165c and a 180. of the three, the 165c and the 180 are by far the best to use, and the 180's screen is actually quite brilliant for its age.

so thats my recommendation. a PB170/180, as they have a good amount of "oomph", are easy work on and have pretty decent keyboards as well as a very awesome trackball.