It is impossible for subtitles to be superior to a well done dub if you do not speak the original language.
It depends on the anime. I have seen some good dubs and I have seen some horrible dubs. Don’t laugh at me but I watched some Yu-Gi-Oh in Japanese and it is horrible, whereas I prefer the Japanese version of FMA over the dub.
I do prefer a good dub over a sub, though. I think it’s just better in terms of not having to read subtitles. Also the quality of the localisation tends to be better, since a lot of fansubs are quite literal in their translation.