Subtitled. Generally the people who get hired to be actors can act better than people who get hired to do voice-overs. Otherwise, they'd get work as actors. Celebrity actors doing voice over for cartoons tend to overact, so you really can't win with a dub.
If I'm watching a movie about Mexico for example (like El Mariachi), I want them to speak fucking Spanish. It's more authentic and I can get into the movie better. If there are a bunch of Mexican characters, in Mexico, speaking english, it pulls me out of the movie (Desperado bugged me in this way). Same goes for any film from any country in the world.
I guess if I had problems reading or something, I would prefer dubs. But to each their own. Most dvds have both, so who cares. Widescreen vs. pan and scan, on the other hand...