Ummm actually, there's quite a few voices in the Slayers dub I can't stand.. Where-as the original voices are great if you ask me.
The best examples are from season 1... In particular Gourry's childhood friend whose name escapes me.. her voice actress did not have any emotion in her voice whatsoever.. always monotone and dumb.
Also, I prefer the VA for Lina in the ADV dubs (Movies, OVAs, etc..) than the TV series Lina.
Oh yeah, and Gourry should NOT sound like a surfer. It's like Surfer Goku, but in a show I actually like a lot! Don't make me make a wave file about Gourry catching some gnarly waves ;P
Apart from that, the Slayers dub is great.
Tenchi dub: Yes does indeed rock.
BTW don't trust the subtitles, they're 80% wrong in all the Tenchi stuff. Don't claim that Japanese VA's are saying something unless you've translated the Japanese yourself... (He does NOT say "Ah!" when opening the door... although I will admit, "Ryoko, it's for you!" is damn funny

)