If you're now thinking about assisted, that opens a whole new world. Personally, I don't like assisted, but Kershaw makes some great ones. As do they as Zero Tolerance as well. Or at least they used to. I can't say I've actually looked at Kershaw or ZT for a couple years now. I prefer Kershaw/ZT assisted openers to Benchmade. When is comes to closing, I have an easier time of closing the Kershaw one-handed. Because of the mechanism they use, you can close them most of the way, the shift your grip to complete the maneuver. Trying that with a Benchmade usually ends up with it opening most of the way again, and I have to start the process from scratch at least once. Benchmade seems to use a coil-spring, whereas Kershaw uses some kind of spring that is almost like a leaf spring in shape. In any case, it has some freeplay that is advantageous in closing. Conversely, if you don't keep the pivot cleaned, oiled, and adjusted properly on the Kershaw, you can end up with them not firing completely open, as they float that last little bit before opening.
My favorites are knives that have either a similar locking system to the Axis lock, where you can pull the lock back and the knife will fall open; or "flipper-opening" knives, whatever their lock type. With the Axis lock, it is for all practical purposes a gravity-opening knife. That can be bad depending on who sees you do it. When in pc company, I can usually pinch the blade open and complete with my thumb on the blade.
OH, I always remove the thumb studs from knife blades. I can't stand them.