1. Disc brakes. If you tour in the mountains you should know that descending down mountains can be dangerous. On extremely steep descents, standard rim brakes will heat up and melt. Whereas disc brakes will cool themselves as they rotate around the caliper. Will you be touring in the mountains? If so make sure you use disc brakes, they are the safest option.
Please understand disc brakes are not perfect, if you bend a rotor they will give resistance and squeak incessantly. Which is amazingly annoying on a tour, so be careful not to bend the rotors.
Overall disc brakes are best for the mountains, however I would not use them on a tour unless they were necessary.
2. V brakes: These are usually standard on mountain bikes and hybrid bikes. They are easier to adjust than the older cantilever brakes. They perform very well in all conditions except extreme descents, and heavy rain. I would normally recommend these brakes, unless you will ride in the mountains or a rainforest.
3. Road brakes: These are the weakest of the group of different brakes, but they will work fine on standard tours ( except for in the mountains ).