Willie Mays was more well rounded than Griffey. I will say that had Junior not had the injuries, he likely has better numbers than Willie Mays, the numbers are very similar.
Mays- 660 HR's, 1903 RBI's, .302 average, 338 stolen bases, 12 Gold Gloves
Griffey, Jr- 630 HR's, 1836 RBI's, .284 average, 184 stolen bases, and 10 Gold Gloves
BUT the best player of all time in my opinion was Babe Ruth. Don't believe me? Check these numbers out:
Ruth- 714 HR's, 2213 RBI's, .342 average, 123 stolen bases, and they didn't have Gold Gloves when Ruth played. His Fielding percentage was .968- pitcher and outfield combined. Which is lower than Griffey- .985 fielding percentage, and Mays- .981 fielding percentage, but Babe Ruth was a pitcher player the outfield. And he did a good job at it- playing the outfield that is. And for my Internet spinning special, Ruth had a fielding percentage of .988 as a pitcher, his natural position.
I have to wonder if the Babe played today if he would be a dual-position DH/OF/closer, because he was a darn good pitcher. He had a career record of 94-46 with a career ERA of 2.28, and then he was 3-0 in the World Series with an ERA of 0.87.