Well, voice acting is really a much bigger industry, and a more respected career choice, in Japan than most other countries, so generally their dubs should be better... even if that isn't always the case.
Now, personally I'm always puzzled by people saying that they can't tell if the acting is good or not when they don't understand the language. My grasp of the Japanese language is absolutely nothing to brag about, but I can still fairly easily tell if the voice acting is good or not. I can read what they're saying, I can hear how they're saying it, and I can tell from the tone and pacing if it's any good.
Also, I almost always prefer to have a film or game in its original language, regardless of what language that is. Chances are higher that the voices fit the characters that way, rather than just being "stock voices" they use for all of their dubs, and production value in general tends to be higher.