Unless you are changing the pots you shouldn't need to remove the knobs. If you do, they will USUALLY just pull right off, so give that a try first. If it seems to be taking excessive force, then you need to find another way. The Stew Mac tool, which I have, is fine, but VERY expensive unless you need it a lot. I actually use it mostly for pulling the anchors for TOM bridges. If you are going to use a flathead screwdriver, you are better off with the largest one which will fit under the knob, as it gives you more surface area. Just be carful with the added leverage. You could easily dent you pickguard. You might want to put a thin piece of wood or something under the fulcrum point to protect the guard. Try working your way around the knob with your prying device, whatever it is. You might also try wiggling the knob - GENTLY - with you hands. Work one edge up, then the opposite, etc.
I have to admit, these days I just grab the Stew Mac Jig.
Light
"Cowards can never be moral."
M.K. Gandhi