When asked once in an interview in Tennis Week magazine who was the toughest doubles opponent she ever faced, Natasha said "Hingis." She said Martina had better disguise on her shots than anyone she'd ever played.
And Zvereva has faced Navratilova.
Hingis in my view gets the nood because of the variety of people with whom she has won slams, the fact that she has that calendar year grand slam (something only three other women have done, Bueno, Navratilova/Shriver) and because Martina was also ruling singles at the time. Natasha, great as she was in doubles, only won four singles titles in her career. Hingis was simultaneously ranked number one in the world in both singles and doubles, something achieved by only four other women. (ASV, Davenport, Navratilova and Clijsters.)
When Natasha played with GiGi, they were an amazing pair. Martina was amazing no matter who she played with (which at the AO in '97, included Natasha.)
Renmenber, Hingis even partnered with Monica Seles, not exactly a legend in doubles, and beat the Williams sisters.
Can you imagine how many doubles titles she might have won had she just been a doubles specialist like Natasha or some of the others?
Indeed, look at Martina's record with Kournikova. They actually played something like 71 matches together and only lost four times. (they were defeated in several other walkovers when one or the other pulled out due to injury.
In terms of number of slam titles and doubles victories, Natasha comes out on top. But Hingis' overall abilities in doubles are simply greater than anyone's other than Navratilova.
And Martina number one pretty much admits that.
After she and Arantxa played and lost to Hingis/Kournilova in Germany in 2001 (I think) Martina N. aid she now felt she played every great player in doubles (during her own lifetime, I assume.)
But Navratilova didn't let it end there. Last fall at Staples Center, in an interview with Eurosport, Navratilova was trying to urge Hingis to come back so they could play doubles together, saying that would really cap off her career.
If you take women players and look at their entire careers, both singles and doubles, Hingis has to rate up there with Navratilova, King and Court.