Depends on your needs...
For example, do you want to avoid WiFi? (Hard to avoid on modern devices, but can be disabled.) Do you need to use your existing PalmOS software? (Only available on the Palm Pre and Palm Pixi, which run PalmOS apps in an emulator.) Do you want text recognition? Do you have a specific price range?
Fill in your requirements and we can make a few recommendations.
Let us know.