In North America, the English Theme is more popular, but in Japan, the Japanese one is. This is because Japanese people hear the Japanese theme on tvTV and Americans hear the English one. In Germany, the German version of Gotta Catch Em All is most likely more popular. Further more
Furthermore, people prefer the one they can understand. For englishEnglish speakers, it is Gotta Catch Em All. For Japanese speakers, it is Mezase Pokemon Master or Aim to be a pokemonPokemon master.
English is more widespread so more people will prefer the English one. I am a native englishEnglish speaker and prefeeprefer the japaneseJapanese theme. This is because I got sick of the English one.