I've always preferred my foreign films subtitled over the dub and this carried over to anime. I think the only time I ever preferred a dub was with "Kiki's Delivery Service" where Phil Hartman seemed better as Jiji than the JP seiyuu (who sounded like a Luna ripoff). Generally though, I see the Japanese as better because there, the Seiyuu are *acting* while the dubbers are *re-enacting.* They focus too much (IMO) on trying to sound similar to the JP instead of making it sound natural in English
In my experience, dubs seem to go to two extremes: 1) Tame everything down if they're trying for a TV slot [Hence, Haruka and Michiru are "cousins"] and 2) Make things as crass as possible if it can't get on mainstream TV [4-letter words in Excel Saga]. Also, sometimes the dubbers miss the point, or give a line connotations that it wasn't supposed to have. With subs, one can see subtleties in humor that dubs completely miss and possibly the translator didn't get. Unfortunately, the examples I discovered are probably too crude to post without my getting banned, so I'll pass.
Finally, the dubbers have a
BAD tendency to try to match the mouthflaps (which the Japanese don't try to do) which means a lot of extra words are added to a line if the Japanese words take longer to say than the English words.
Anyway, these are my reasons for my preferences and I'm not trying to start a sub vs. dub war. I have no problem with people who like dubs so long as I have access to subs.