PALM OS vs Mobile Linux vs Windows Mobile 2003 vs PocketPC

[Fox5]

Which one is the best OS and why, and what are the problems with the others?
I've been looking at the Tapwave Zodiac which uses Palm.(but it seems it doesn't work with generic palm hardware, and palm's software support isn't as good as pocketpc?) Stupid $80 keyboard appears to be the only keyboard available for it.....

Sharp Zaurus with Mobile Linux....however these devices are a bit rough around the edges, and the high power ones are very expensive.

Windows Mobile 2003 on the Dell X30, which seems to pack a lot of power. Of course, I'd imagine software selection is even more limited on this since it isn't a true version of windows, but it does appear to have a full version of microsoft word and excel(probably complete with spell check), and I'm not sure if other pdas would offer similar functionality.(in word)

And I haven't seen anything using PocketPC that caught my eye, but just noticed that many reviews of Palm devices basically fault them for not being pocketpc.