Here's one point of view, from Thorn, which heavily favors 26-inch wheels for loaded touring but makes bike in both sizes.
http://www.thorncycles.co.uk/why26inchwheels.html

Thorn's view (as I understand it) is that for heavily loaded touring and partial off-road touring 26-inch wheels are better (stronger, more suited to fatter tires, etc.).

For light touring or sport riding they say it is a toss-up or better for 700c.

One practical problem is that 700c rims and tires can be difficult to find outside the US and Europe.

Interestingly, Rodriguez has 700c tires on their standard touring bikes but 26-inch wheels on their W2 touring bike, which is made with S&S couplers. Their argument is partly that with 26-inch wheels the bike is easier to fit inside the traveling case.

www.rodcycle.com


Co-motion now has a 26-inch model, the Pangea, for expedition touring. On the other hand, REI changed their "heavy duty" touring bike, the Safari, to 700c from 26-inch this year.