All other things being equal, a "20K" or "extended protection" version of a product is usually a "better" formula than its "non-extended-life" ... but that depends on whether BITOG can agree on what constitutes "better" as it depends on application...
The Dexos 1 Gen3 + "20K miles" claims on the ultimate bottle mean that the oil is likely starting off with a higher TBN and better consideration for modern engine concerns like LSPI and aftertreatment compatibility. I would expect that to be the better oil. With that said, it's always possible they put the real magic in the other bottle and just decided not to take credit for it....