Not sure how much weight I'd give any particular fight in judging Lewis' or any other fighters rating. Ali had some terrible fights that if you just picked the one fight would make you wonder why he's rated so high, same could be said about Louis and pretty much any other ATG heavyweight. As to whether or not this was he best win, I think there's a distinction in that it may be his most important win, as opposed to his best performance. I certainly think the destroying of Golota, Ruddock, Grant and Rahman, are far more impressive fights in terms of Lewis' performance. But sometimes, he, like other fighters, just do what is necessary to get the "w". Certainly one could also argue he should have been more aggressive against Tua as well, but for better or worse, Lewis figured a completely dominating performance without the risk of getting KO'd was a better option.
I think the hesitance to open up on a hurt man is actually often a riskier business than trying to get him out of there. And combined with other instances of carelessness it's a flaw in a fighter's make-up. But Lewis got away with it against Holyfield. And he should have got the "W". But is that all we need to know to rate these fighters ? I'm not so sure. Lewis's defeat to Rahman was, IMO, a result of errors in the ring, and an amateurish over-confidence, and not just bad preparation.