There's no all-encompassing answer to which is better, because localizations are not always superior and neither are the originals. It depends! Ichigo Mashimaro is an example of an anime with an English dub that makes no sense at times, ruins the humor, and is just plain unlistenable, so Japanese voices/English subtitles are preferred. Pokemon is an example of an anime with an English dub that is awesome and more fun than the original!

Some other examples: Spirited Away has a great English dub, but Howl's Moving Castle has a very unfitting one (Billy Crystal as Calcifer is the worst part), which I can't stand to listen to.

I'm pretty wary of dubs in general, though.