Well, it depends on 2 things: what you want a PDA for and how much you have to spend.
If you are budget constrained, forget a PocketPC device. They tend to run in the $500US + range. They are also a passable substitution for a laptop, provided your intended use is email, light .doc/.xls viewing/editing, MP3 playback, contact/scheduling, etc.
If you want a replacement for your Franklin Planner, go with a Palm. They'll do all the other stuff too, with the right app and/or widget add-on. The pricy ones are in the $250-$350 range, and the inexpensive ones are sub-$120, iirc.
The best way to figure out which is for you is to nab your tech-toy buddy and goof with his. Barring that, head down to CompUSA/Staples/OfficeMax/Wherever and futz with their display models. That way you can check out how they feel and fit your hand along with their capabilities.
Hope this helps!
"That which does not kill me, makes me stronger." -- Friedrich Nietzsche
"That which does not kill me, missed." -- Anonymous war gamer