I personally would most likely go with something Palm based. There are several reasons why which include:
More stable than Windows Mobile
Doesn't have all the features that I wouldn't use
Palm support is one of the best I have ever used
But in defence of Windows Mobile there are a few things that stand out in my mind that would make it a good choice also:
Greater functionality, more program options
Microsoft is ever expanding (Limitless potential)
I guess bottom line, if I were looking for something more business related which is what I normally do I would most likely go Palm. But from a personal standpoint I might would look into the Windows based products more simply because the features for play are there.