You beat me to it, was about to quote this from an earlier QotD. 
But to give a more serious answer: Japanese (with English subtitles). Not only are they the original intended voices, but they’re also released a few weeks earlier than the English dubs.
I actually used to watch the anime in the English dub, but eventually they were 3-4 weeks behind, so I switched from dubs to subs (midway through the XY era). Haven’t looked back. (I also watch all other anime in Japanese with English subs anyway.)
Greetz,
Quuador