I'll go with Moon, since I prefer Lunala, although both versions have Pokemon that I like better than their counterparts (Passimian>Oranguru, Alolan Ninetales>Alolan Sandslash, but Drampa>Turtonator, and Celesteela>Kartana).
Ultra Sun since i opted for the bigger amount of available pokemon species. I just only recently bought Switch Lite and Pokemon Sword way back then. Then a year later i decided to get 3DS and i bought Pokemon Omega Ruby first. I do admit the default Nintendo Micro SD Card is absolutely tiny for Pokemon Omega Ruby + the update and demo for Mega Glalie.
Later i bough Ultra Sun and Pokemon X as digital versions. Too bad the ash-greninja demo was so limited.