I prefer disks as they engage my thumb the easiest, most securely, and most reliably. I don't mind studs or holes, but prefer studs over holes. Holes are easier to find for me, but my thumb more positively engages studs than holes. My thumb tends to slip on holes...a bad thing when combined with a lockback as the blade draws closed resulting in cuts in my hand. So, my heiarchy is disks, then studs, then holes. I've never had a stud or disk catch in my pocket when removing, but they do catch when closing, which isn't really a problem.
My wife prefers flippers, be it manual or assisted (tho, she likes AO).