Definitely Witcher. It's no surprise the Polish version would be better given that it's a Polish game based on Polish books, so it's closer to the original and more easily retains the original style and mood, but it goes beyond that. The polish voice cast is really great, especially the aboslutely perfect Geralt, whose voice I find frankly just terrible in the english version. I have no idea what they were even going for there. It's like some Clint Eastwood parody mixed with a bad impression of Adam Jensen from Deus Ex.

[insert Japanese game here]

Many of the japanese or anime inspire games are better with japanese voiceovers imho.

I prefer the French version of Outcast over the English version.
I prefer the Japanese version (with subtitles) when available over any other versions.

I like the voice of the narrators in Trine (Italian) and Candle (Spanish).

:)
I'll keep that one in mind, when I get to it in the back-log. I wonder if my Norwegian will be up to it.