Hmmm,
I'd say MeDeFe (for carrying on in-depth debates in a foreign language)
Guiscard (highly academic and logical)
Backglass (skillful use of emotional appeal-in spite of my best effort to knock him off his game plan

)
Bertros Bertros & chronus (who solidly back up their statements with citations)
OnlyAmbrose (one of the few people who appears to be equally comfortable in science, mathematics, philosophy, and theology)
luns & flasheg8 both (excellent use of humor to incite and diffuse situations alternately)
and
Skittles (for coming up with delightfully intricate ethical puzzles)
others up there: daddy1gringo, Mr. Nate, vtmarik, colossus, chronus, Heavycola.
Ooops, I forgot 2dimes........ sorry dude.