I went to a girls grammar, many moons ago, and loved it.
I meet up with several of the girls from my class each year (we're mid 50s now) and we all look back fondly on those days, even though we have become friends as adults now.
dh went to a mixed school
Neither of us felt strongly about wanting / not wanting single sex for our dc, but, when we looked at options locally, the schools that were the best fit for my dc happened to be single sex.
I would 100% make the same decision again.
ds, in particular really thrived in his school. He is quite 'bright' (in a quick to understand things sort of way, and top sets sort of a way) but not 'academic' in that he doesn't like studying, he has ADHD and completely lacks time planning and organisational ability. The staff at his school with one notable exception really 'got him'. Obviously I have no 'control' as to whether this was because they were used to teaching all boys, all the time, or whether they were just a great staff.
In truth, dd1 would have thrived at the boys' school
. They had a real emphasis on outdoor ed and that would have suited her down to the ground.
Both dds went to a girls' school, and there was nothing about it being a girls' school that made it a bad experience. I mean, I do have issues with some things, but nothing to do with the fact there were no boys there.
All went to mixed 6th form.
I think, crucially, all did hobbies / mixed with both boys and girls throughout their teens outside school, and I do think that is important anyway, but is particularly important if they go to a single sex school.