Dang, why couldn't you ask an easy question?
I like the design of the M16 (in fact I like a great many of Kit Carson's designs) and I wouldn't be surprised to hear of it having the better lock, but i've also heard alot about CRKT's AUS6M not performing to acceptable levels - it was enough to scare me away from the F4 I was originally planning on getting.
The kershaw is a little different, it's a small frame lock - frame locks are usually strong but to be honest I haven't examined this one personally, I would hypothesize that because of it's dimunitive dimensions, the frame isn't much thicker than the average liner-lock... the blade as far as I know is a well-heat treated 420HC, not the greatest stuff in the world but don't be fooled, a well heat treated 420HC can whoop badly heat treated AUS6M anyday of the week - as my Camillus 420HC Arclite clearly proves.
And speaking of Camillus products... let me throw something in the pot you perhaps didn't consider: how about a Camillus Sierra? Those knives are fantastic folders for the money - the only really downside is they can't be one-hand closed in a particularly practical manner, but the quality of their heat treat is so excellent Camillus 420HC acts more like 440A! Also i'm almost sure that the Sierra would have a stronger lock than the Vapor or M16-Z. Just something to consider.