Subs most of the time, no matter what. The most dubs are horrible (at least in german).
There are indeed some animes that got amazing dubs (like Attack No. 1/Mila Superstar or Dragonball), I've enjoyed these in my main language. But if you exclude this old animes for nostalgia, I'd go with the original version all the time.
For me, it has to be subs. The only time I went out of my way to try a dub, it was for Shuffle!, and it was horrible. Our girls make a normal line into a screeching sound that makes my ears bleed. But on the other hand, sometimes you get too focused on a Sub's subtitles, and could miss some important details on screen.
Some animes that are dubbed have decent/horrible voice acting and some anime that are subbed with the original voice actor is just horrible/great. My vote goes with both.
Iv always prefered dubs just because I'm to lazy to read subs. If Im gonna read it, i may as well just read the manga. But i always hate it when people try to compare the dubbed version to the subbed version of the same anime. If you watched the sub, why are you watching the dub? Ill admit, some dubs are just pain bad, but some stuff translates well and get great dubbings. K-on and Lucky Star come to mind right away and we all know that Cowboy Beebop is on of the best dubs ever. So to the elitists who only repeat what the other uneducated elitists keep saying, "Cuz the voicing acting sux," get a clue and try some of the good shit or find a new reason to prefer subs. Its cool if you just prefer it, and dont really have a reason, but dont just spout ignorant garbage about the quality of dubs that you've never seen.
I have to say both. There are a lot of subs that are better than the dubs but there's still a few dubs that are better like cromartie high. The sub wasn't nearly as funny.