While I might agree *a bit* with Doggonit's colorful and insightful analysis of PocketPC's in general, I would never recommend a SONY to anyone.
Having said that, the Toshiba's do appear to be the top dogs for PPC's right now... then again, wait 3-6 months and it'll probably be another mfg or model number.
I'd say get the one that does what you want it to right now, and worry about future capabilities later. Another theory is buy a fairly cheap one that barely meets your minimums, but then get a new one in 12-18 months or so (start a cylcle like that).
I mean, if a top of the line is $600 (let's say), but there are $200 units, that's basically getting a new unit every year for the cheaper ones, but once every 3 years for the expensive one (and I don't know many people that have PPC's over 3 years old). I dumped mine (iPAQ 3635) about a year after getting it. I went back to Palm because I needed dependability more than flash and pizaz. But that's me.