Better to install ducts on the inside of home walls, or outside the walls then encase them in drywall?

I added a heat duct to an old farmhouse I had back in Ohio. I ran the duct in a corner of an extra room built a frame around it and sheetrocked it. It looked fine. Obviously in the wall is ideal if your doing several but you will need to choose your walls carefully. Pick walls that dont have plumbing. That should be very easy as most walls dont have plumbing except in a kitchen or in a bathroom wall. The worst thing that can happen is you will find a wire that is running to an outlet. This can be easily relocated around the duct. Its really just preference. If you choose outside the walls you are going to be seeing it as long as you live there and probably someday wishing you had put it in the wall. If your insulation in your walls was blown in instead of using roll insulation, prepare for a mess when they cut the wall open. Good Luck.