The guys at TheTechZone have posted a PDA & Handheld buying guide. It's a decent five pages of what you should look for in your next PDA purchase. I'd say go with a phone-slash-PDA if you're going to make a purchase anytime soon.

"The Personal Data Assistant (PDA) has won rapid acceptance among university students and executives who are constantly on the move because of its ability to package a lot of different data requirements into a palm sized device. "