Based of the USDA’s NCGR-Corvallis Mespilus Catalog, it seems they believe ‘Macrocarpa,’ ‘Nottingham’ and ‘Marron’ to all be synonyms. Of the three I’ve only eaten ‘Macrocarpa’ (lots of it), but regardless of whether all three are actually the same clone or not, if they’re at least similar enough to tentatively be synonyms I’d have to say they’re all my top pick.
https://www.ars.usda.gov/ARSUserFiles/20721500/catalogs/mescult.html