In general terms oil that meets an API spec is about the same as any other oil that meets the same spec. They can be mixed and matched to your heart's content. An oil company must stop when it meets the spec because to invest more in time and resources would cause unneeded expenses and really cut into profits because they sell a lot of the stuff. Good enough is good enough. In fact, these oil companies often buy their base stock and additives from the same suppliers. You might be getting virtually the same exact oil with a different label. Let marketing fill in the fluff and present the product. Today cars most often fall apart, lose their appeal or rust away before the engine fails.
Today's 4-cycle gasoline poppet valve fuel injected engine using current engine oil is a marvel of design, development and mass production. It's been around for over 100 years and so far has resisted a takeover by any number of proposed replacements. As more challenges appear the good ole fashioned 4-cycle engine shows that it still has the "right stuff" and there's more to come.
Now, to answer your question. The only reasonable variables left for a given API spec are price and availability. Buy the cheapest, on sale oil that meets viscosity and spec's required for your application.