I'm on my second (now quite old) Ipaq. This one's a 5555. It does all I ask of it, but it's slow when the tasks get complex. It's got the whole of our Churchyard records on it - full details of about 6,000 burials - which is a file several MB large. It takes a couple of minutes to load, but once that's done, it's brilliant.
It's not crashed in a long time (but does do so). IO540 is spot on with his analysis.
I'm not sure there's a lot to choose between the brands - they tend to leapfrog each other as developments proceed. Way back, I had a Psion 3a which I reckoned was a pretty nifty bit of kit. It's quietly decomposing in a drawer somewhere now.
I'm very glad I chose the Ipaq and a separate (small) cellphone. I don't carry the brick (Ipaq) in my pocket when I don't need to. Having looked at "all in one" devices like Blackberries, I prefer my way!