Nikon, Canon, Olympus, Sony, Pentax should all be considered. What feels most comfortable to you is important. The best camera is the one you have with you; it is the one you are willing to take all the time for backpacking. I was Nikon SLR user since the early '70's and then Nikon P&S digital. But I ended up with a Sony DSLR (since my lenses wouldn't work with Nikon DSLR's, that was both good and bad news). And a number of old Minolta lenses work great with the Sony.

As for the micro 4/3, I have a problem since they don't have a viewfinder. Perhaps I am just old school, but I want a viewfinder to compose my pics and also not worry about the LCD being unviewable due to the sun.