I am digging thumbdisks myself, as I find them to be a safe method over studs. If you slip up, you thumb is already higher on the blade, avoiding a nasty run-in with the blade edge. That being said, it also has to do with the knife model and where the disk is placed. Some are not so great in that regard. An example of a thumbdisk that for me is in perfect alignment is RJ Martin's Avenger. It has plenty of access from both right and left hand and swings the blade open fast and sure.
For studs, I am digging the ones provided by Johnny Stout. They have rubber inserts that are real grabby and, coupled with smooth action and the arc of opening, makes for a fast and safe opener.