Lubrication's primary objective is to provide a hydrodynamic film between metallic (in your case) moving objects. Secondary objectives are protection from corrosion and water expulsion, among others. The basic objective is met pretty easily. However the longevity to which that objective is met is where the real secrets lie. Oils break down through heat and shear forces. The hydrocarbon chains become reactive at temperature and tend to break their hydrogen bonds. They also shear, like a pair of wire cutters and a length of wire. To combat this different manufactures add different performance packages which are almost certainly proprietary. To that end, short of being a chemical engineer for all the companies, you can't be certain which oil is the best. I have found however, in a free market economy the more expensive oil TENDS (but not always) to be the better oil. To be perfectly honest though we are talking about details, and most oils with todays computer monitoring systems will perform more than satisfactorily. So, to sum up, you're best off just buying the oil that fits your budget.
