UA prefers SFO over LAX unless there is a massive gap in O&D. For traffic to "business cities" like SIN or PVG, the difference is smaller due to SFO's large tech industry. For more "leisure" and VFR cities, the difference can be massive because the LA area has a much larger population than the Bay Area. MEL is probably the exception to this rule because SFO-MEL is pushing the range on the Dreamliner, and UA did not know the capabilities of the Dreamliner a few years ago like it does today. UA credited LAX-MEL as being the reason they knew the Dreamliner could handle SFO-SIN.