With the lockback, what I'm most concerned about is white-knuckling failures. So I white knuckle the handle and see if my palm engages the lock (which it does on something like 25%-40% of lockbacks). If it passes this test, I'll usually prefer the lockback no matter how the liner lock fails.
With the liner lock, I test for white knuckling, spine pressure, and torquing. Even if it passes, I have 2 other worries. First, many liner locks will eventually fail during a torquing test (unless they have very big washers up front; unfortunately, most don't). Holding the knife in your hand and torquing with just hand pressure is usually the only test you can do in front of the dealer. However, as I was remind a couple weeks ago while I cut up cardboard, in real life you can end up torquing the blade much MUCH harder. A guy sent me email a few months ago and told me his liner lock failed due to torquing while cutting cardboard, and he ended up with stitches. Obviously, his lock showed no torquing problems prior to this, and I bet just torquing the blade in your hand wouldn't have shown any problems. Luckily, I was using an Axis when doing my cardboard cutting.
Anyway, problem #2 is I've personally seen liner locks that passed all tests for years (in my case) suddenly start failing one day. Other people have told me they've seen the same thing. This worries me -- will my rock solid knife suddenly start failing because the washers have worn a little bit or the liner has worn at a weird angle?
The AFCK is my fave 4" liner lock production folder BY FAR. I'd still take the lockback.
Joe