^ In terms of hosting an AC - which UK YC makes the most sense IYO?
Wrong question, the YC wouldn't have much to do with the logistics.
Royal Cornwall is (amazingly enough) in Cornwall and 5-6 hours from London. No local airport. I grew up in Cornwall and it felt like a long, long way from everywhere. Still does.
Royal Yacht Squadon (RYS) has a prominent club-house at Cowes overlooking the Solent. It is a working club that runs some major events. It is also ultra-establishment with a more than nominal connection to the Royals.
Royal Thames has a large club-house in a posh part of London and many members with a City (finance industry) connection. Despite the location, it is probably more active as a racing club than the RYS.
I know members of both, have visited both quite often. Never have been or will be a member of either. FWIW I probably find the RYS the friendlier of the two.