I've tried listening to Slipknot over and over and over and... well... you get the picture here! They just can't trigger any emotion for me... and that's sad for a band I think! Ok, maybe 'Wait and Bleed' makes me twitch a little, but that's it... =/
As for Korn, I really like a lot of their songs! And their video 'Twisted Transistor' featuring all those rappers is simply AWESOME! Not to mention the song itself which has a great echo-ing ring to it! =D
I'd have to go for Korn as the better choice here... they simply have something that makes me stop and listen, something I will never have with Slipknot I guess... I don't know if it's the whole song layout, their lead singer's voice, their style in music, their videos... heck, why not all of it!?! LOL =)