I say sub and dub both have their pros and cons, not just on anime but on movie as well. Dub is only good when the voice actor and translator know what they are doing and keep the meaning of the dialogue as close as possible since some foreign languages have a deeper meaning in their wording. If done right, the dub verison is as good as the original. One that comes to my mind is Neighborhood Totoro and Spirit Away. Or The Good, The Bad, and The Ugly is to me, better than the original language.
As for sub, they are sometimes annoying read and even an ammature could make one. You always need to do your research to find the best one or hope for your favorite fansub to sub it. And remember, the translator for the fansub are not someone who have a bachelor degree in japanese so even the best fansub can mess up.
So, really it is ups and downs. If it is backed by a corporation like Spirit Away is dubbed and distributed by Disney, then you know the dub verison is good. If it is ADV, Fanimation, or etc, then I go with sub.