I always thought the buck 110 had a great lock up, but from my research it looks like the Tri Ad is really lock to beat now. In fact they say it's so strong that the blade will break before the lock ever does. My next knife is going to be either a Voyager or Recon 1 to test it out.
I'm leaning in the same direction with a Cold Steel Espada with Polished G10 Handle.