To me, it depends on my mood and the anime. XD
Like Digimon, I grew up watching the dub, so I prefer the dub. TMoHS I really liked the dub on it cause I liked the voice actors, Romeo x Juliet I like the sub, I don't even know if there is a dub out there. Same for Strawberry Panic and Junjou Romantica. So really... it depends. And if I really like an anime, I will watch both and compare them :3