Three way...

[Mad Scientist]

I gave The Kids In the Hall the nod. However, they had the benefit of a finite lifespan for their show and far fewer episodes per season than the competition. Personally, I think that SNL has improved greatly since Tina Fey became head writer ~1.5 yrs ago. MadTV is tolerable and occasionally gets it right, but I can't stand some of their skits (such as the Kenny Rogers ones). I don't like to waste my time on parody when it is poorly executed; undeserved ridicule makes it even worse.
That's my $0.02.
-MS

[foehammer]

Indeed, I find MAD TV unfunny and annoying almost all the time. I've only seen one episode of Kids in the Hall and didn't find that funny either. Weekend Update ALWAYS has at least one hilarious snippet, though again the old ones were better. So SNL gets my vote.
R.I.P. Chris Farley and John Belushi...