I've got a Palm M130. Great for my needs and handles the geocaching information that I've needed so far. It's not as advanced a unit as some though.
I don't know much about the new Palm Tungsten's, but from my research and experience I would suggest the following:
1) If you are looking for a good device to keep track of appointments, addresses, dates, task list, misc things such as geocaching information, some downloaded web pages, etc. then the Palm with an OS operating system and good battery life has worked fine for me.
2) If you are looking to download and keep pictures, maybe take pictures, listen and download mp3 files, more graphical type things, then you may want to look at a unit with the windows operating system.
These were the biggest issues when I bought mine. You may also want to check out www.cnet.com
They have reviews, good/bad comparisons, feature comparisons, and they will give editor selections. Good source of reviews for all computer, digital camera, and entertainment systems. Hope this helps.