I definitely prefer the hole.
I won't even rate a first, second third list. I simply don't like the studs, and I'm not sure what discs are. Are they the semicircles that are mounted on the spine of the blade near the hinge? If so, nah, don't like 'em either.
My dislike for the stud and disc comes from a personal belief that simplicity is always best. Fewer parts, fewer joints, fewer fasteners -- better. It's why I like Spyderco (holes) and it's why I like Glock. (Glock makes a point of having as few parts as possible.) I really don't like the idea of a *hole* being drilled into the blade just to screw in a stud. And they are never as ergonomically correct (in my limited experience with studs) as holes. I've handled lots of stud knives at gun shows and found they didn't work in my hand well. Practice could help this, but why bother when holes fit just right? Besides, where there's a screw, there's a screw that could *loosen* inadvertently. I've also seen mention of cracks that form in the thin strip of blade steel between the stud and the spine of some knives. Why risk it?
Someone mentioned oval holes over round holes, and I am inclined to agree that the oval hole on my 555 Griptilian (mini) is aesthetically superior to any round hole on any of my Spydercos.