When I watch Pixar and Disney films I always try to find the English version instead of the Swedish dubbed one. Lip synked or not it feels like the natural thing to see it at it was done originally.
It was natural to me to think the same way about Ghibli movies. Of couse I wanted to have the original voices. Or: that's what I thought. Now I'm not as dogmatic about it anymore, not after watching My neighbour Totoro. The Japanese voices in that film ripped my ears into pieces. They were just too high and shrill, to the extent that they distracted me. I couldn't think about anything else but how much I hated them. And that's not a good way to watch a movie. So after 20 min or so I gave up on it and watched the movie dubbed. The relief! Now I could enjoy it.
I've watched other Gibli movies with Japanese voices and Swedish subtitles. So my response is: it depends. On a principal level I'd rather watch the original, but there are exceptions, when you just can't stand the voice in question,and in those cases I see no wrong going with other voices.