The Rock was awesome on the mic. He was funny as hell. He had great charisma in and out of the ring. His in-ring work was NOT the best for technical moves, but he also never hurt anyone, so other wrestlers should have loved working with him. His Sharpshooter is a great piece of evidence on how he was technically not a good wrestler. I still loved to watch his work, but it was more about his charisma than his moves.
Austin was also gold on the mic. He was also funny as hell. His charisma was off the charts. He could really work any kind of match well, but he was more of a brawler. His matches with Bret Hart were epic. He and Vince really defined the Attitude Era. There were many involved, but his long program with VKM put the E back on top.
So this question is really too vague. On a pure wrestling standpoint, Stone Cold wins. Rock was close behind, but he WAS behind SCSA. On a "Hollywood-famous" standpoint, the Rock wins easily. I love Dwayne on the big screen. He's really one of the best action stars that we have currently, and he can do comedy well, too. Kinda like Schwarzenegger could do.
Being a wrestling purist, and this being the PW sub-forun, I have to vote Steve Austin. I enjoyed both of their work with the E, but Austin was more of a draw for me than Dwayne was.