The brake choice shouldn't swing your bike decision either way, but if all else equal on your bike choice, I'd go with disc brakes. On multi-day rides, often don't have a choice about riding in the rain and the braking performance in rain is much better. Often on the same bike model, the disc version will allow wider tires - another plus for touring. Carrying extra pads is no harder than carrying extra rim brake pads. Just about every bike shop carries and repairs disc brakes these days.