The lockback is the strongest.
Of course, there's Andrew Demko's Tri-Ad lock which combines the compressive strength attributes of crossbar locks with the other strengths of a back lock. And there are push button release compression locks, as seen on Kevin Smock's SK23 and the Spyderco mass produced version of the same. I'm sure there are others I'm forgetting about at this hour.The crossbar locks like the Axis are the stronger than lockbacks that can wear and release. Many here don't trust poorly executed liner locks, with good reason, since they have the reputation for failing. There are other interesting locks like the compression lock that are strong and reliable and the button locks are just a version of a crossbar lock.