I feel much stronger about the other voices though... the guy who throws him in is much better as a Glaswegian IMO. There is also the fact that the UK voices are the original ones. =)
I understand that the UK version is the original, and therefore why that's the version GOG has made available, but I still maintain that the US protagonist sounds better than the UK protagonist.
As for the other characters, I would be unable to call it. I had only a demo of the game (US), limited to the confines of the apartment, so the only voices I experienced were Kent's and the guy who threw him in. I imagine that Kent has far more lines than other characters, so I'd rather decide between the protagonist's voice then that of other characters.
Sadly, I don't forsee GOG offering the US audio track, since English is still English.