As long as you are willing to give up some manual control, any of these will stand up to your travels just fine.

I'd eliminate the Oly models, given their continued use of xD cards, with their verrry slow speeds and 2G capacity limit. The Panny is so new nobody's tested it yet. It and the Pentax both have 28mm equivalent lenses, which is a big plus over the ususal 35mm or so maximum. If you have time, I'd compare the two models after some tests reveal whether their image quality is up to snuff. Specwise, they look darn similar.

Cheers