It depends on the reason I'm watching it. If I'm watching it because I want to know the story I'll usually watch subbed. If I'm just watching it because a friend told me so, or for background noise I'll usually watch dubbed.

I always hear people say subbed is automatically superior to dubbed, but I've seen some really bad subs too. There was one anime I watched about japanese folklore and in the subs it refereed to Tengu as "black crow goblin demons" instead of Tengu, or "Crow Demons", or even "Heavenly Dog" because what tengu technically translates to. Onibi were called "Baby fire demons" versus Onibi or Will o' Wisps (The kanji for Onibi 鬼火 can be translate to Will o' Wisps").