I'm surprised no-one's mentioned the Como Group here.
15 or 20 hotels worldwide, and those I've stayed in in London and Thailand are truly outstanding. The Group is owned by a Singaporean billionairesse apparently, so she's under zero pressure to sell up to a huge Group like Hilton or Marriott.
St Regis and RC sadly, still, for me, have the feel of the "chain" product that they are. Though I'm sure there are outliers in both cases where they manage to retain the bespoke boutique style of service on offer in places like the Connaught in London or the Royal Mansour in Marrakesh to give but two privately owned examples I've stayed at recently.
But I have high hope for Al Maha, which I'm staying at this coming winter, and is part of Starriott.