Chavez, but it's closer than the schmucks above would have you believe. Tyson was a monster. Flat out. If you disagree you're a hater.
I don't see how anyone couldn't choose Chavez. Hugely better longevity and resume. Not close, really.
Tyson's wins were just as good as the best of Chavez wins. Neither guy beat the cream of the crop, but Tyson does have wins over Spinks and Holmes and Chavez does not have many wins over that quality. Even Meldrick Taylor was not the level of Spinks and Holmes to me, although he was more at Chavez weight and age than Spinks or Holmes to Tyson. Chavez was more consistent but I think Mike more dominant. This is a tough one. Maybe Chavez barely.
Julio César Chávez has greater accomplishments. Tyson may be higher head-to-head in his own division, heavyweight. Chávez should be higher pound-for-pound.