Pocket PC all the way. I've had both the original Palm Tungsten T, and the Dell Axim X30. I know they are a few years apart, but even a T|3 or T|5 is relatively similar to my original T|T. Palm (both PalmOne and PalmSource) just don't get it. With a Pocket PC, you get Bluetooth, WiFi (a must, really), more expandability options...the list goes on.
Like several previous posters have said, a Palm is just an organizer, with barely any multimedia capabilities. A Pocket PC is genuinely a pocket sized computer. I know MS gets flak for Windows on the desktop, but I think they've done a great job with Windows Mobile (and that's saying something, since I'm a Mac bigot!)
Palm has dropped the ball. None of their current PDA's include built-in WiFi. This was really the deal breaker for me. WiFi is everywhere! They want to charge you $350-$400 for a PDA, then charge you an additional $120 for a WiFi card? That's absurd. Granted, the screen resolution on the T|3 and T|5 is better than the standard Pocket PC resolution, but that's just not enough to warrant the higher price and less features. (You can now get VGA resolution on Pocket PC's too.)
You can get a 624 MHz Dell Axim X30 (which I had and was very pleased with), with built-in Bluetooth and WiFi, plus excellent multimedia/internet features, for under $300. You can't get many of those features on any Palm, at any price. The $400 T|5 doesn't even have a voice recorder.
I also purchased Mark/Space's Missing Sync, which works great. You can sync over WiFi, which is much faster than Bluetooth. All you do is press one button on the Pocket PC, and without even touching your Mac, or launching the Missing Sync program, your Pocket PC shows up as a network drive on your desktop and iSync launches and syncs. Works really well. Only hitch is that some programs require you to run an .exe to install it onto the Pocket PC. If you don't have access to a PC or VirtualPC, you're out of luck.
In conclusion, you get so much more with Pocket PC. I don't see how Palm can compete. And, on the same lines, this year was the first year where Pocket PC shipments exceeded Palm shipments.