My first real knife was a Kershaw Whirlwind, and I've since owned two more as well as a Leek. Because of this, I was initially inclined toward the thumb stud. I even tried some thumbholes and thought the thumbstud just made more sense, as well as felt more natural.
Then I bought a Spyderco. I had tried them before and dismissed them for various reasons including the "hole". However, after just one week of using the Spyderhole I found myself liking it more than the stud and wondered to myself why I took so long to see the light.
That said, everyone is different, and one must figure out what will work best for himself. I've bought many knives in my quest to find the one that suites all my needs. In that experience I learned that what works for one person may not suite another person. I also learned that limiting myself to just one knife is just limiting myself, since "one" knife can't meet "all" my needs. Some will prefer the stud, and some will prefer the hole. There is no such thing as "The Best", but there may well be a knife opening mechanism that suites your specific needs better than other knife mechanisms.
I don't know about the "hole" being faster than AO. Personally, I no longer "flick" my knives as I consider it a bad habit for me to get into. If your looking for the fastest opening method then get the "wave". It is currently the fastest, and that is an absolute. This isn't a plug for Emerson Knives, or the wave. You asked about fast opening methods, and such a discussion would be lacking without mention of the wave. I will say that if you decide on the wave, that you please respect the intelectual property. The wave is an Emerson design/idea. There are companies who are shamelessly "ripping off" this IP, and they should be avoided.