I would guess best depends on what you want from the pedal. I like the Lunar Module and Screwdriver here. I would not mind finding one of his muff style pedals for a reasonable price but have not been lucky with the search so far.
id say Screw Driver, because of its versatility. I can get a nice fat lead fuzz out of it like on my Lunar Module, without it getting over the top. That being said, its a HYBRID fuzz/od. so it really doesnt count.
I've had the good fortune to have owned four Skreddy pedals and currently own three.
I agree that the Screw Driver is a unique pedal but not really a true fuzz tone. That said, I think it's Skreddy's best pedal.
For fuzz I really like the Lunar Module. It is very flexible and has geat tone no matter how you dail it. I had the Mayo for a while, but the Dice Works Finale was better so the Mayo was traded away. The Mayo was still an excellent pedal worthy of the praise it gets.
Skreddy makes some of the best pedals ever made in my book.
Lately, I've been dividing my time between the cogdisII and the lunar mod dlx. Both are incredible. That being said, for nastier fuzz, the zero, ernie, and ?lady each do unique and wonderful things. I have yet to try a mayo, mayonaisse, or pink flesh. I've had a couple screw drivers that didn't do it for me and a top fuel that I'll probably sell when my pigmine arrives....