I usually watch in English, though my preference for the later seasons is Russian, the first season is absolutely abysmal. Luna is called "Moon Pony". Literally. Wat. Wat?
Plus Russian has a lot of fandubs for pretty much anything even remotely well-known, down to 80s and 90s shows from America.
I've also watched episodes in French, German, Polish, Swedish, and Belorussian. I enjoyed the Swedish spitfire so so so much, but I think I preferred Polish the most out of these. Sad thing though about Belorussian is that it will not get listened to by anyone. It lags far behind Ukrainian and Ukrainian is completely uncompetitive with Russian.
Generally the reason a lot of people watch shows in the original language is voice (Applejack) and jokes that don't translate well. In some sense, if something is made towards a general (international) audience, I sort of dislike regionalisms that make translation even worse. It's much better to play jokes off of characters than languages. It just cuts of a lot of potential.