Page had awesome hand speed for his size but was often out of shape. His hand speed in the ams was crazy. He, Holmes and Dokes were the three fastest heavyweights in their time with Tubbs coming on a little later.
Hard thing to measure based on the different distances guys would throw there shots ect. I'd pick Louis though all his shots where powerful, very short and crisp.
You can see a lot of guys throw dazzling, super fast flurries that carry next to little or no power. Say Fighter A. That’s an extreme example but doing same can be relatively easier than throwing quality shots whilst still maintaining excellent speed. Say Fighter B for the latter case. So you could say fighter A is literally faster but lacking balance in his punching in terms of quality as compared to fighter B. And, if fighter A did actually properly commit to his shots in overall terms, he may find himself not even as fast as Fighter B. For all the technique, commitment, leverage and power behind his punches, I think Louis was exceptionally fast and just plain fast any which way (absolute terms).