How many lock type are there?
I have Walker Liner Locks, Leafspring Lock(like the kind on the TL-29 Style Electricians knife), Bolt Lock, Lock Back, Mid Lock, Boye style Mid Lock, Push Button Lock, Frame Lock, Axis Lock, Rollox Lock, Toggle Lock, Compression Lock, Saddle Lock(?), Butterfly Knife type lock, so many more my addled brain can't remember right now but if I had to pick a favorite, it would be the rock solid, smooth as silk Axis Lock on my BM 730 Ares.
I don't test my locks to see where they fail, basically if I'm usin' a knife and that is ever a fear, (that it might fail) I wouldn't use a folder, I'd use a fixed blade. The locks to me are more of a redundent safety for my own stupidity if I'm usin' the wrong tool for the wrong job.
Don't get me wrong, I can appreciate a well fit liner lock or the snickin' sound ya get from a lock back, the complexity of the Paul Lock, the rachetin' sound of a Navaja(?), or the rock solid thunk, almost like the sound of a vault closin', that ya get from a perfectly executed frame lock.
I guess they're all my favorites when I have 'em in my pocket.