As David said, it depends on where and how you want to ride and possibly your inseam. If you have a short inseam, you may be forced to go with 26" wheels.
Another pro for wider tires and touring is that if you have wider tires (50mm+), you can get a mini-suspension but keeping the tires not fully inflated. This is nice say on chipseal roads or small gravel. Additionally, if you like to bring the kitchen sink, wide tires can typically support more weight compared to narrower tires. For stronger wheels (you carry the kitchen sink, heavy rider, etc.), 26" wheels are stronger than 700c when all things the same.
A plus for 26" is that you very well might have a lower standover height. This is good if you bring your leg over the top tube vs. over the saddle as sometimes after a long day, that little extra inch of height causes me to snag my heel.
If you plan on staying in North America or Europe 700c will be available pretty easily. Plus, 700c/29er tires are marginally better on gravel and/or bumpy roads due to larger diameter.
Realistically, if you ride in NA or Europe and are not super heavy and carry a ton of gear (say 300+ pounds for bike, gear, and rider), either will work. The heavier you get, the more spokes and/or smaller rim you need to have strong enough wheels.
Both sizes have a decent selection of tires to choose from.
Tailwinds, John