Control over The One Ring

[Legolas]

Who says that Gandalf is greater than Sauron?

I didn't. The quote I provided (and the statement I made after it, which you quoted) did not say Gandalf was greater than Sauron. It said Gandalf was equal to Sauron in their beginnings:

To the overthrow of Morgoth he [Manwë] sent his herald Eönwë. To the defeat of Sauron would he not then send some lesser (but mighty) spirit of the angelic people, one coëval and equal, doubtless, with Sauron in their beginnings, but not more? Olórin was his name. But of Olórin we shall never know more than he revealed in Gandalf.

I did not break it down into specific areas. I assert that Gandalf as a whole was greater than Saruman. Willpower, wisdom, skill...everything figures into an overall person. One person may better another in certain areas, but the other may be greater overall still. I did not mean to imply that Gandalf was stronger than Saruman in very possible attribute.