Definitely Mary. She's an album-woman, where I think Beyonce is more concerned with strong singles than with strong, cohesive records on the whole. And those are the ones that become classics, IMO.
Mary, period. Alicia's IIAGY, YDKMN, Woman's Worth, Fallin', Diary, LYNSMA (and TSWABH sort of) are classic to me tbh. I don't really see myself listening to any Bey chunes years from now. I'll remember Bey as a fierce performer, morseo than for her music.