Sub - generally find Ash's voice unbearable to listen to, sadly. Also it feels like any subtlety in the writing (and it's not a subtle show, but it does have moments) is gone, and the performances become more broad with less scope for more quiet, considered delivery that you get in the original. In the dub, everything seems loud, all the time. Also the music is always better in the original broadcast, by far.
I prefer the original version by so much that I'd actually rather watch it unsubbed, and just kind of figure out what's going on, than watch the dub.