I would double-check with hospitals and institutions at which you will be training. They may use a wireless system for patient labs, med record, etc. that only use Palm (or Windows). Ways to find out may be to call the med school, check its website, check the websites of the hospitals or call/email their IT dept. You don't want to be stuck with a PDA that you can't use during third and fourth year.
Apart from that, I have found more medical applications for my Palm OS device than I did for my previous Dell Pocket PC. I am sure that now many applications are available for both.
Bluetooth and/or WiFi would probably be necessary if you are accessing a hospital's system. Both Palm and PPC offer these.
If you're a Mac user only the Palm will sync with it out of the box.
Internal memory may not be as important as whether it has an expansion card slot. I can fit a ton of reference texts on my 512mb SD card (not to photos, songs, games, etc, and it is still not filled). That said, at least 64mb internal memory on the device would be nice. Again, these are common in both
Finally, I have found the Palm more intuitive to use. The Palm TX sounds like it would fit your needs. The Dell Axim X50v also seems pretty solid.