Here is a link to the poll: http://www.strawpoll.me/14848150
When I say "solo" I do not include playing two-handed; there is only one investigator.
I play on easy. When playing multiplayer I usually play on standard, but for solo it seems like there's a severe action disadvantage that other mechanics do not compensate for well, so standard is actually harder than advertised. Thus I scale back to easy.