I love this perennial topic and have scoured the forums and internet for years.
just adding my $0.02.
caveat: I have sort of wide but small feet (like a hobbit, I suppose, but without the hairiness) and have an okay tolerance for pain, need minimal arch support, and my weakness is shoes. ;)
all the shoes listed here have been well broken into prior to the respective trips ...
2013 - honeymoon Paris/Nice/Barcelona early fall:
Merrell's Mary Jane sneakers -> wore on the plane
2 pairs of ECCO gladiator sandals (black and pewter)
1 pair black AGL flats
2018 London/Paris mid-fall:
1 pair of black Vans (soft, like sneakers) -> wore on the plane
1 pair of black Tory Burch Revas
1 pair of red Tieks
1 pair of black stiletto heels (NEVER walked to and from in them - only carried them in my bag to change out on 2 evenings out)
to each her/his own, but thought this might be useful for anyone looking for comfort + a bit of fashion. not an expert by any means, only offering my experience :)