I was inclined to say Bonds, with his combination of speed and power...he did have some power prior to moving to the Giants. But Mickey Mantle played CF during most of his productive years, while Barry did play some CF, he didn't have the overall defensive skills of Mickey.
I still think it was Bonds, but I don't have the hard data to back it up. And there are plenty of variables, like Mickey playing in Yankee stadium as a switch hitter, using the hitter friendly RF porch...while Bonds played in less hitter friendly Pittsburgh.