It mostly depends on how you plan to use it and how much you want to spend.
If you're looking for the basic PDA functions (notes, calendar, etc.) and don't want to spend a bunch of money then Palm is the way to go.
If you're looking to use more advanced functions (multimedia, voice, wireless, etc.) then you could choose either and plan to spend a fair bit for that functionality. CE would probably be the better option in the mid to high end of the multimedia capability spectrum. The Dell models can often be found on sale if you monitor the internet deal forums.
I've used both for many years and prefer Palm because I'm pretty proficient at the Graffiti input method, they seem to be more stable, have a larger number of available applications and can generally be purchased inexpensively, new or used, especially used.
My advice if you're looking to get started using one and don't want to spend much would be to pick up the Palm z22 ($99 max) and try it out.
Good luck and I hope this was helpful.