All three are pretty solid options.
Best upgrade option: probably the St Regis. Suite upgrades at the SGS in particular are very hard to get because of the loyalty of a lot of Bonvoy elites
Lounge offering: Probably the Athenee
Breakfast: Not sure, probably the St Regis
That said, my preference out of the three is the SGS. It's just a really nice hotel, even if the service levels weren't yet at pre-Covid levels when I was last there.