My experience is that PDA users are as loyal to particular brand of PDA as the Windows vs. Linux people, the PCs vs. Macs people, and the old Atari vs. Amiga wars.
Because of that, I'm going to try to stay clear of singing the praises of Pocket PC over Psions or Palms, or any other type of PDA. All I will say on the matter is that I've been a Psion 5 user for a number of years, and although I still use, and like my Psion, I find that it's inclusion of a keyboard makes it just that bit too big to carry around on a daily basis...