getting a ppc (like all other electronic devices) is a very personal decision... and to be honest, i'm not so up-to-date with them (i have a toshiba, but it's partly due to brand loyalty -- Dell Axim x30 seems popular, since i've seen a couple people in my class with them). try brighthand.com for some recommendations and reviews. honestly though, all of the modern ppc's (i.e., those using the Windows Mobile 2003 OS - either 1st or 2nd edition) will do everything you want it to... i would just make sure that there is SD compatibility and at least 300mHz processor (which are moot points actually, since ALL of the ppc's since 2003 have been sporting these stats). and as for med school apps and programs, at least at my school, ppc is supported more than palm (though i don't know if that's the norm).
with the newer handhelds, you also have options like Bluetooth and WiFi. unless you have other Bluetooth-enabled devices, this connectivity option on a handheld is useless (and unless you're a gadget-freak like me, you're probably not going to use it anyway if you have it). and as for WiFi, i'm actually against it, because i think it's a novelty; it's one of those things that are really cool (and can be convenient if you're dying to access the net), but not that practical. in most cases, the included IE in ppc's don't display webpages correctly on the small screen anyway (so it's a lot of scrolling). personally, i wirelessly connect my handheld to my Nokia smartphone, and access the internet via GPRS; it's slower, but you get much better coverage and it's essentially the same thing as built-in WiFi.
