I currently own a Verellen Skyhammer 100 watt head. I am looking at getting a used marshall dsl 100. I would like to use both on stage but have them eq'd completely differently to have a dynamic sound. Which way would work best for this: slaving one of the heads off of another one, or just run one from the stereo output of one of my effects pedals?
Slaving one into the other gives you the opposite effect: you're using one to amplify the other, so you wouldn't get two distinct sounds at all.

If you want that two amp layered sound, you want to separate them as much as possible. Running both heads off a stereo output is a good idea, and if possible you'll want to use two separate cabs instead of two halves of a stereo cab.
yeah i have 2 100 watt cabs, 1 2x12, 1 4x12. I plan on running the verellen through the 4x12 and the marshall through the 2x12. The last pedal in my chain is a boss dd7 with two outputs, I plan on just running from that.