I'm one of the few Spyderco fans that prefers frame-locks, probably. It's hard to explain the appeal, or why 75% of the custom folder market is made up of frame-locks and liner-locks. The R.I.L. isn't necessarily the strongest lock around, but a well-executed titanium frame-lock is still plenty tough, and I'd wager a knife like the K2 could stand up to all the Demko-designed abuse a Cold Steel does, and hold a lot of weight. The Slysz Bowie is a perfect example of a frame-lock done right; strong, not a hint of galling, a snappy detent, and most grips reinforce the lock (I'm not sure what kind of vicious twisting you'd have to subject the knife to for the lock-bar to be accidentally disengaged, but I wouldn't say it's impossible). It's also allows for a very smooth, free action, which is why it's so often paired with flippers.
While I prefer the titanium frame-lock as an all-around combination of smooth action and snappy detent, simplicity and aesthetic appeal, strength and reliability, I don't think it's the top performer in terms of brute strength. The spine-lock and close relatives like the 'power-lock' or 'triad-lock' have proven themselves to be incredibly tough and reliable. The Endura, Stretch and Caly 3.5 are all great knives, but I find the placement inconvenient for quick one-handed opening, and the action is stiff and slow. You can still flick them open, and it's not a concern for some, but it's not really for me.
The compression-lock is a design I like as much as the Ti frame-lock, and in some ways more -- you get the same near-frictionless deployment and snappy detent, a flow-through construction, and very quick, very easy one-handed opening and closing; but I believe the compression-lock on the Paramilitary 2 and Yojimbo 2 could be the strongest available. Could be. The ball-bearing lock on the Manix 2 is another great Spyderco innovation, but I feel the compression-lock is their most impressive design.
