Canon FD is excellent. The older breech-lock lenses are "heavy duty", the new FD type lenses are super compact and fit well with mirrorless digital.
I have used all sorts of lenses in the last years. Comparing FD to Nikon I simply fail to see why Nikon was considered "pro" back then while Canon FD (or Minolta) was not.
I also remember Leica guru Erwin Puts stating on his website, that if there would not have been Leica he would have chosen Canon as a system. The FD series had the edge in optics back then, according to him.