I do prefer to watch subs because different show's dubs vary in quality from "as good as the original seiyuus" to "that's a bit annoying" to "painfully bad", but sometimes there is no choice (for example, anime on Netflix Instant Watch is dub-only, and some movies in theaters are only shown dubbed) so I have learned to be flexible.
I watch dubbed versions of animes mostly of those shows that I saw already and just want to know how they made with dubbing.
Yeah, it's interesting to compare the two sometimes. I just bought the box set of Kuragehime/Princess Jellyfish and I'm really looking forward to finding out how they handled the "ore/olé" jokes. I remember comparing the Japanese dialogue and the dub on the DVD version of Hare+Guu (this was a few years back, when I was mainly learning Japanese from comparing subs to dialogue) and there is a part where Guu says "マザコン" and the dub says "You have an Oedipus complex!". It takes some effort to fit an eight-syllable sentence into the space of a four-syllable word!
I also agree with Hopey that some dubs are really good. I haven't seen the Chobits anime but both FMA's dub were good. In the last episode of the first FMA there is a somewhat infamous part where a character was dubbed as saying "I love you" when it wasn't explicitly stated in the Japanese dialogue, which was just "Watashi..." or something. However, I think there is enough context/subtext to show that she had a major crush even without her saying it outright, so I'm not pissed off about the added words. My brother complained that Al sounded "like a girl" in the dub of Brotherhood, but I honestly don't agree. Even though I know that they had a girl voice him this time around, he doesn't sound girly to me.
But maybe he just has a better ear for voices than me: when we were watching TTGL dub together (he has bad eyesight, so he can't really read subtitles) he was the one who realized Nia's voice was the same person who voiced Starfire, even though I'm as big a fan of Teen Titans as he is.
Speaking of dubs and subs, anybody know of any video games that give you an option to play them with dubs or subs for character dialogue? The only one I know is Eternal Sonata/Trusty Bell but I really liked the option.
Wow this turned into a long post.
Mami chibi drawn by Jiino, animated by me. | Sophie sig by Misuzu | My Anime-Planet page
but you know, not every image has a source and not every character has a name :3