Did Whitaker have the best footwork of any fighter?

I'd certainly rate Frazier and Ali below Whitaker here. Frazier was as good at cutting off the ring as anyone ever, but he didn't have much in terms of moving backwards. Ali had a bit too much a preference to retreat in straight lines to really compare to Whitaker, IMO. At least in a technical sense. His combination of speed and balance was extraordinary, though, and he could punch off his movement as well as Whitaker, which is quite extraordinary for a HW.

 

Whitaker was also good at cutting the ring off. That together with his ability going backwards makes me favour his footwork of Frazier's.

But as a pure pressure fighter very few can compare to Frazier.

This may be splitting hairs, but I would rather say that punching and defence is a function of footwork.

Ali is always tricky in this kind of comparisons, since he wasn't that text book. But perhaps you could say that the moving back in straight lines that he sometimes did is evened out by Whitaker's crossing of his feet.

One could say that Ali's athletecism and not his tecnique was what made his footwork spectacular, and while there's some truth to this I think it's a gross oversimplification. Anyway, you're right that Ali's footwork at his peak made him "lethal", i e nigh impossible to beat. Whitaker perhaps wasn't as dependant on his footwork, but that may be down to him being a more complete fighter rather than his footwork being inferior.