I'd take Joe...and some observations on Tyson
Joe Louis would probably beat Lennox. Remember you'd have to set your wayback machine or time machine to get them in the same place at the same time, which would affect training methods. I would say Joe Louis would be quite fearsome with today's training regimens, and would probably come in at around 215 at least. As for Lennox, if you put him back in time he might be less effective because he'd probably weigh more, and would in fact be slower. In other words, Lennox today is as good as he'd ever be, but put Joe in today's age and he'd be better. I agree that Joe's right hand would do it.
Now as far as Tyson goes: the fact is that he peaked as a fighter in the late eighties. When Don King moved in after the deaths of Jacobs and D'Amato, eventually leading to the dismissal of the competent but not great Rooney, Tyson's technique went south. He was losing his defensive skills and was firing wildly even when he fought Bruno the FIRST time back in '89. Tyson's last great fight was against Michael Spinks in 1988--yes, fourteen years ago! If you look at his record since then he has not had one truly great win since. I've heard the "he was on drugs" excuse forever, even back to the Douglas fight, but unfortunately the loss of Tyson's technique was his real undoing. When he became easier to hit he stopped being dominant, and that whole thing didn't get any better when he went to prison the first time. Then Evander--who everyone thought was past his prime anyway--beat Tyson soundly, and Mike was really done after that.
By the time Lewis got to him, Tyson was a glorified punching bag with only a vague puncher's chance of winning. In Tyson's first few great years Tyson-Lewis would have been a cool matchup, but even then you wonder how Tyson would have done if Lewis wasn't intimidated by him. Every good fighter who has faced up to Tyson has defeated him, which to me keeps Tyson from true greatness. As mentioned earlier, Ali, Frazier, Holmes, Louis etc. all had defining fights where they turned the tide. Every time Tyson has been faced with real adversity, he's lost.