26" is fine, but don't consider riding unless you have front suspension. Otherwise you'll have numb hands and lose your mind. Full-suspension sucks if you suspect that you'll be riding on a variety of surfaces, from smooth to rough. Let out some air pressure, have wide-ish tires (>1.75") and just ride.
I spend 4 months touring through Mexico, and stuggled to find rough roads. Conditions are much better down there than expected. The toughest stuff I found was in Baja and Oaxaca. Rest is fancy paved roads, albeit oftentimes quiet and remote...