I would happily live in Marylebone, it's lovely and has a brilliant high street and some green space.
Fitzrovia is fun particularly around Charlotte Street but does always feel kind of polluted with a lot of traffic.
Mayfair I know very well. Some lovely bits around Mount Street Gardens, particularly the mews streets. However I don't personally feel it has much community feel.
Belgravia very grand, kind of sterile. But I would love to live in one of the smaller streets like Kinnerton Street or maybe just off Elizabeth Street. A bit similar to Chelsea, possibly.
Bloomsbury I like. Lots of students, lots of garden squares. Coram's Field if you have kids.
Lots of these areas are super busy but there are smaller back streets and mews houses which are quiet.
I would also consider St John's Wood which is a little less central but only 2 stops to Bond Street or a walk through beautiful Regent's Park. Some streets in Covent Garden and also the South Bank which is very buzzy, well connected and has the river right there.
Chelsea is lovely but not well connected at all, lots of other options for you.
Have never lived myself in any of these but a Londoner all my life and have worked with residential properties in some of these locations.
Not sure why people are being unhelpful, why shouldn't you live somewhere great. The problem is with those who buy these homes and are barely ever there because it's just an investment and they have five others.