Definitely sub due to usually better quality VAs, as well as some really serious lines just sound really terrible in English. I don't usually actively read subs. Over the time I've watched anime, my mind just kind of acknowledges it's there, while focusing more on the visuals, and can get 99% of what they are saying. If I'm really tired though, I'll have to go back to reading them. Not to mention, dubs just aren't as available as subs are, and you have to wait a lot longer for them most of the time.