Regarding the classic jazz and pop song stylists who sang the Great American Songbook:
When it comes to female vocalists, there are so many that I love - Billie Holiday, Peggy Lee, Ella, June Christy, Julie London, Anita O'Day, Dinah, Jo Stafford, the list goes on. There are so many good ones that it is hard if not impossible for me to rank them in any kind of meaningful order.
However, when it comes to male vocalists, I easily place Frank at the VERY top, and think there is a really steep drop until you hit the next level. I don't mean to knock any of the other male singers; I love Tony Bennett, Mel Torme, many others, but I think Frank is in a class all by himself. Some would say Tony is a close second. I think he's nearly as good at the rhythmic, uptempo stuff, but as a ballad singer, I don't think he's half as great as Frank.
Not trying to create a let's-trash-male-vocalists thread; I just think this is an interesting dichotomy.