The point of having a huge open world to explore is to explore it and look for treasure and stuff in all those little dungeons which define the series (and will hopefully still be present in the usual numbers). As a result I will tend towards travelling overland to begin with while I explore, but as I clear out areas of the map and so on I plan to fast travel through those areas as there will be less point in walking through places I've already explored.
If you fast travel constantly, right from the beginning, your going to miss half the game, but at the same time when you get to the point where your going to be doing the "Ultima Workout" you know find a clue/quest, travel to the other side of the world, etc... that's where fast travel becomes useful.