I know everyone has a favorite, and I would really like to hear from the metallurgists and chemists on the board.
The problem is they don't shoot guns. I listen to guys who have about 100 world shooting titles and send a million rounds a year downrange like Brian Enos, Todd Jarrett, Rob Leatham, Chip McCormick, et al. They actually knows what keeps guns cycling and reduces wear. They use (and in some cases make their own) lubes and use grease in their guns.
As for liquid oils, FP-10 is the best OVERALL performer because it gets good marks for lubrication, rust prevention, and cleaning ability. As for pure slickness of an oil, I have tested most and found Militec metal conditioner to be the slickest as measured by trigger pull reduction. But, Militec is a poor rust preventer. Nothing is perfect.
Overall, liquid lubes of any kind suffer the effects of gravity: they run downhill and off where you put them. I've heard all about how even after they are gone they leave behind a molecular film...... that doesn't make me feel real confident for protection against metal shear as on slide rails and sear faces.
I settled on using a 50-50 mix of a liquid lube and a high tech grease. I mix FP-10 or Militec liquid into Rig+p grease or Brian Enos Slide Glide. Basically, grease is a thickened suspension that has lubricant trapped in it so it holds it where you put it. The wear in my guns dropped drastically since I switched to the new high tech greases blended with oil and I shoot my guns a lot. The down side of using grease is that it's not idiot proof. In colder weather, you have to dial down the viscosity (with liquid lube) to make sure the gun cycles properly. I believe a 50-50 mix like I use would be good down to temps much colder than you would want to be out in.