Were I Uber Wealthy, I'd likely pick California, probably SF, maybe even LA. There are parts of both cities that are prime, I've seen more upscale places in LA than SF. And yeah, I'm talking billionaire wealth. Helo to take me to John Wayne to fly to Zurich or Geneva on a lark. If we open the options to outside the US, the question gets tougher.
Sonoma county might work.
It wouldn't be Paris or London, for me. Monaco? Maybe, a lot of tourists. Singapore? Maybe, kinda hot. Sydney? Never been. Buenos Aires? They have good air.
Rio? Been there, didn't like it at all.