There's enough good ones here that it makes judging harder. First, here are some of the best for each strip:
Diesel Sweeties
481182
481373
I don't know who Rachel Rosen is, and Red Robot C-63 isn't gay, but it was still funny.
Pearls Before Swine
480699
I'm surprised no one used Rat. He gets some of the best lines. Still, it is usually the stupid crocs who are funniest.
Sinfest
481223
This also has IndiePete from Deisel Sweeties in it, but the others are Sinfest characters. It's hilarious how God sometimes mocks the Devil with his hand puppets, especially when he's trying to conduct the serious business of getting someone to sell his soul.
And the winner is RCCOLAMAN for the Sinfest strip. I laughed more at this than at the others. Good job.