When we stayed at the Dolphin, we always walked to Epcot. It's a pleasant walk, and it seemed to me with the other stops and as slow as the boats go, we walked it quicker.
We did take the boats to MGM, although that is also a pleasant walk, just longer. If you have kids, my boys loved riding the boat.
I'm not sure how often they run, but we never had to wait more than maybe 10 minutes, and we were there at a busy time.