Requires a lot of both. I'm a competitive swimmer myself and as far as endurance goes, it really depends on the events you swim. Sprinters have to worry more about the technical things like the start, turn and finish. Endurance swimmers have to train to keep a fast pace for a long period of time.
However, I can easily say that an incredible amount of disipline is required either way. You have to mentally push yourself to beat that guy next to you. Even during practice you have to have disipline and push yourself to do the best you can.
i like baseball, im a pitcher, and i can honestly say thats the reason i play the sport, pitching is so much fun. i like soccer and golf more. I really dont watch too much sports, mainly because i dont watch a whole lot of TV, and when i do watch tv i can always find something funny or cool to watch.