I've an iPAQ and a T68i - both sync with the PC at home (and iPAQ syncs with work too). Excellent, I love both.
You've to ask yourself what you're gonna use it for - certainly you get more oomph with the PocketPC but this costs you size, money and the battery life can be a pain.
On the other hand, with PalmOS machines, you have often less functionality but there is a lot of applets out there.
If you're going for a PalmOS machine then the Sony is the one - especially with the virtual graffiti zone on the screen.
If you want PocketPC then look at the iPAQ, Pocket Loox etc - there are many challengers out there....!!
Alternately, you could do what my missus has just done and get a Nokia 9210i communicator - also a good machine (but no bluetooth nor GPRS).
If I was to replace my iPAQ, I'd look for something running Windows for PocketPC 2002 with a good screen, 64Mb or more RAM, bluetooth and SD card slot. A CF slot would be good, especially if it was built-in....