When it comes to live-action films, I prefer subs; I find characters' mouths not moving in sync with their speech much more distracting than reading a few lines, especially since I'm a fast reader.
When it comes to anime, I usually prefer dubs, with a few exceptions. I find that Japanese voice actors always seem to overact, and the voice of the actor rarely seems to fit the character in my opinion. In addition, for anime that's set in English-speaking parts of the world, like Hellsing, a dub actually makes more sense; the characters would be speaking English, not Japanese. I still prefer translations that stick as close as possible to the original dialogue, rather than taking massive liberties as many companies did in the past.
