Oil is superior to grease when it comes to mechanical wear properties. Period. Grease is base oil, additives, and a thickening agent. It is the additives (and to a lesser extent the base oil) that determine the mechanical properties. Other than the increased viscosity which allows it to stay put compared to an oil, grease has no increased ability to fight wear or shear or sliding friction. In fact these thickening agents tend to diminish the properties of the additives and oil. This is not voodoo or opinion, but textbook Tribology, covered in various engineering disciplines, and the foundation for the whole field of lubrication engineering.
Saying that "for high wear points, you need grease" is simply untrue. Thats not to say that grease isn't extremely useful in certain circumstances; it is indeed. However, most of these conditions are not found within the operating mechanisms of personal smallarms. I use it sparingly, for places like choke tubes, or inside the mainspring housings of 1911's. It is also handy for storage purposes, where its resistence to evaporation over long periods of time is actually useful. I can see arguments for using it inside the mechanisms of revolvers, where dirt and grit are less able to contaminate it.
For most weapons and environments, however, oil will give superior lubrication properties. Despite the fact that the best oils leave a unseen boundry film that protects the metal, many people need to see their lubricant in order to believe that it is effective. Instead of using grease, increase the frequency of your maintence and lubrication regimen until your weapons appear satisfactorily clean and lubed (this doesn't include bare metal guns dripping oil though).
That being said, I use and recommend MPC FP-10 on frame rails (almost everything else too). Aside from lubrication and cleaning abilities, informal tests have shown it to be one of the best at preventing rust too, followed by Eezox and Breakfree CLP which I would recommend (in that order) if FP-10 was unavailable. When I need grease, I use MPC lithium grease or <gasp!> tetra grease. Despite modern theories to the contrary, FP-10 has yet to cause an explosion due to incidental contact with Tetra grease. I've been very impressed with Slide Glide, but there seems to be little test data out on it and it is,after all, still grease.