An interesting question, Dave, and certainly very relevant.
FWIW I visit both fairly regularly : here and Britmodeller for websites and WNW Fans, Airfix, Revell and LSP on social on FB. However on Fb I adopt a nom de plume (Sam Spade) as I'm also a member of various local social media sites and the vitriol that is thrown around is quite staggering - issues like Scottish Independence bring out the very worst in my fellow citizens, and anonymity is worth preserving!
Probably due to the well run ownership of the websites, they tend to be very civilised fora, whereas FB can be a bit of a bearpit and some members seem to feel they have to post boring lengthy novels about why they are right and others wrong. However FB allows 'likes' or emogees to be posted against entries which guage public opinion pretty quickly.
I'm a bit of a joker and find FB great for a quick funny reply or picture which usually goes down well, but the swastika ban etc is annoying (although probably understandable).
Also some sites are run by very intolerant administrators with 'ban-hammers' being wielded against anything that doesn't fit their own particular world view.
I see a place for both: if an FB site closed I'd find another, if this website closed I'd be distraught 😩
Sandy