Uhhhh they are all different. The Q is a smart phone, similar to the Blackberry but different operating systems. The Ipaqs out there are all PDA phones, and have very different specs. The Treos (most) run the PALM OS and are PDA phones...
And to answer your question: The HTC TyTN is the best of them all in this very vague category you seem to be targeting. It'll cost you about $800 though, though you'll get almost everything you could want in a convergeance device. (Minus the massive bulk, lack of Xenon flash, good but not good enough camera, lack of 3.5mm jack)