Neil Sedaka LOL.

But seriously, his falsetto recording of "Laughter in the Rain" ranks it among the best of the '70's (even if the song is kinda sappy).
A bunch of excellent choices by everyone.
If I had to make a case for Sinatra as #1, it would be that his recording career was amazingly consistent and durable, making records and performing live practically non-stop for 30+ years. Even though his vast catalog contains remakes and different renditions of songs he'd sung for years, he had recorded an incredibly large amount of songs, many of them American pop classics.
Here are some more amazing voices:
Hank Williams Sr.
Aaron Neville
Louis Armstrong
Johnny Cash
Freddie Mercury
Phil Collins (just kidding

)