For non-auto & non-assisted, I'd have to say the Spyderco P'Kal. You just draw out of your pocket & it's open. Other than that, I'd say a good flipper, A/O, or auto is going to be pretty darn fast.
For flippers, I've found the Kershaw RAM to be great, a broken in Groove isn't bad, either. I also thought the DDR Maxx Q1A was pretty quick & smooth, too.
For A/O, just about anything Kershaw makes works well. Having said that, I have a B/M Nitrous mini-Stryker that's definitely the equal of my Kershaw Random Leek.
For manual openers, both of the custom folders that I own are darn smooth & quick. They're a Bauchop Shaman & a Jim Matthes tanto folder. Great knives.