Very good tall fighters tend to fight almost exactly the same way. They tend to know how to fight tall! They tend to have KO power with one or both hands, and tend to be high output type, come-forward type of fighters, with very limited lateral and head movement, to a point of being labelled as one-dimensional (relative probably to a slick fighter like Mayweather or SRL). There are not many good tall fighters. Among the tall fighters, who should stand the tallest (not literal height)? Thomas "the Hitman" Hearns, Alexis Arguello, Diego Corrales, Celestino Caballero, Paul Williams, Valuev, are just a few examples of good tall fighters. How good really is Corrales relative to the other tall fighters? He is still an enigma to me actually because he is one of those tall fighters who never fights tall.
I don't think paul williams is a great tall fighter in the way that he uses his height, he could use it more to his advantage. The fighter that uses his height the best is wlad i think.
I'd argue for Arguello, because Hearns was all too willing to forget about fighting tall and get into close range wars. Hearns would be my number 2 though.
Thomas Hearns was the best tall fighter. Then Arguello and Bob Foster. I cannot rate the Klitchkos because they are tall and big. I think being so much bigger gives them an advantage. Hearns and Arguello and Foster fought at weight limits which made that height a detriment if their opponents could capitalize.
Another fighter who hasn't been mentioned yet is Oscar DeLaHoya at 130/135. He was VERY good in these weight ranges and his jab and hand speed allowed him to measure distance and dominate people. He was also an ATG at 147 but he wasn't quite as 'tall' at this weight as this thread would want.