If you look at Boxing.com's all time top 10 HW's, Tyson is 10th & Lewis 4th. Holyfield is 11th. Its always subjective no matter what anyone says. Some experts will look at certain fighter stats and base their decisions on them whereas others will base their opinion on another series of stats.
Im no Bert Sugar, i grew up in the Tyson era so thats whats prominent to me. His style, his speed, his skills, his brute power and relentness pursuit of a violent stoppage are a better combination than anything ive seen after. What came before is up for debate, nobody will ever know how Marciano, Ali, Liston, Johnson etc would have matched up.
Its always subjective.