I'm 90% sure there isn't an official list. But for international
companies, they have what they call the "gold standard" list. This
list includes includes the Kirov, Bolshoi, Paris Opera Ballet,
Royal Ballet, Royal Danish Ballet, and New York City Ballet, in
which case NYCB would clearly be among the top 15 in the US. But
for the others, a list of that sort would most likely just cause a
lot of arguing.