The answer is, "it really depends." The selection of the best bearing lubricant (whether grease or oil) will depend on the application conditions. With a wide variety of greases and oils available, solutions are available for most applications; however, there is no perfect grease whether natural, synthetic, micro-filtered or otherwise.
Every grease has strengths and weaknesses in its performance and consequential monetary costs. For example, high temperature greases typically can't handle high loads very well. "Quiet" greases may break down at high temperatures. Additives have benefits but some drawbacks too. So there is no single best grease for bearings; it really comes down to the application and what characteristics are most important (and which are less).