I think 26 inch is better for touring but you'll get lots of argument on this and the differences are not great. Both are good choices for touring. But you can't just throw a 26 inch wheel onto a frame built for 700c wheels without running into problems. Even if the brakes would reach (and you have cantilevers, right?), the drop in BB height may well mean you will clip your cranks when cornering (which is no fun unless you happen to like falling).