I have recently tried both the Garmin iQue and an iPaq (with external Bluetooth GPS receiver from Emtac).
I handed back the Garmin, and stayed with the ipaq. Let me give give a +/- list from the point of view of iQue:
++ integrated package, no wires :-)
++ easier for beginners (no "systems integration" but also no choices :-()
-- less software available compared to iPaq PPC, for which you can buy several packages for street navigation (I bought Tomtom Navigator), and several packages for off-road navigation, and especially geocaching (Oziexplorer, Navio, Cachedragon, GPXSonar are my favourites).
HansN
I learned a lot about ipaq and GPS (and what to choose and how to integrate) on
www.gpspassion.com and their forum.