For me, it depends on the anime/what I'm doing when I watch it.
For example, I hate the dubbed version of Madoka because I dislike their voice actors, and the anime is fairly short, so I exclusively watch subbed.
Fairy Tail, however, I like to watch the dubbed version because there are so many episodes, and I love how quirky the English voice actors sound compared to the more serious dubbed voices. It's a light-hearted anime; therefore, I enjoy hearing it that way. ^^