Vintersorg is definately more emotional with his singing...and I think he trys to expand his ground as a singer, like hes always trying new things and approaching different ways of using his voice...even if he doesnt have the best tone. But on the other hand, the tone of Vortex's clean vocals are so fucking righteous is crazy. In the song Colossus, his vocals just make me feel like picking up a massive sword and charging head on at whatever life has to offer.
So um, Vintersorg takes the cake...more so because what he does with his voice and who he is as a person.
ALSO...I agree with the guy who said Vortex sucks in Dimmu. It's definately a shame his mighty vocal power isn't getting used that much, but I guess you have to figure in that hes also the bass guitar player. Plus...Dimmu Borgir isn't the same type of artistic band that Borknagar is, Dimmu is more of a darker, angry, crunchy riffing black metal band...so melodies and clean vocals probably don't play as big a role as the grim, demented vocals and disturbing images that Dimmu produces.