I have only made one round trip with them - August 2015 while on holiday in France, my former boss decided he wanted a team getogther in Hartford. Had I been coming from home, it would have been SQ via Frankfurt (and I did consider driving there to get the onward flight to NY but the missus vetoed that!), so it was choice of AF or some US airline.
In the end I decided AF to Boston.
I felt that the crew, though reasonably good on service, had a rather relaxed attitude to seatbelts, bags on the floor, wandering around the cabin during lumpy conditions, whereas SQ crews are much more strict in those sort of areas so it did make me wonder about the whole safety culture. I go to France a lot and they do seem more laissez faire about personal safety, seeming to believe in the individual making his/her own decisions.