There are now 40 gyn oncology programs in the country that take 3-4 years to finish after a 4 year residency in OB/GYN. The evaluation of "best" program is always limited to some subjective interpretation. I do strongly believe that a program that takes the best care of patients is truly the best.
That said MD Anderson, Sloan Kettering, Brown, UNC, and UVA are very strong programs as well as UAB, Miami, and Hopkins.