I own a Military (440v version) and 4 variations of the SS Police model. I like the liner on my Millie, and the flat grind, but of the two, I carry the Police far, far more. There's something about the Police model that makes it not only rock-solid but particularly classy as well. I also own lockbacks that are a few decades old and still lock up fine, despite having endured lots of daily use. I'm not sure a liner lock would hold up over time as well. I'm not sure about sheer strength; so long as a liner doesn't pop off the mating surface, it's very strong. And I've had a (cheap, no-name) lockback's lock fail on me when the notch on the blade back wore to the point that the lever slid over it like a slip-joint, and I've heard a couple of instances where a lockback's lockbar sheared off, but overall, between the two, for a working folder I'd generally prefer a lockback to a liner lock, all things being equal.
Jim
Jim