I think we have already seen AJ's best and it was just enough to get past old fighters in Wlad and Povektin, meaning he'd probably lose these fight is Wlad and Povetkin were in their primes. Vitali's engaging style and hard to predict defense would be too much for AJ, who has a tendency to slow down in the later rounds. VK wins via later round TKO.
Vitali Klitschko wins. Anthony Joshua could barely scrape past Wladimir Klitschko, who was old, inactive and had already been knocked out 3 times. Vitali Klitschko was never down, and part of that was because he was able to use his length and lean back like no other. Stylistically, his defence was hardly exemplary, but it was awkward and difficult to deal with. It was unorthodox and difficult to prepare for. Vitali had no issue with roughing it up on the inside and fighting his way out of close quarters without having to clinch continuously, like his brother. That in itself would take its toll on Anthony Joshua's questionable stamina.
Vitali has a better chin. Vitali could weather the storm and go after him in later rounds. Vitali TKO 9
Joshua. He's more talented and has a better boxing brain. He's proved to be a multi dimensional fighter inside the ring and out of it - in terms of implementing different gameplans. Vitali was limited and had no punch variation. Joshua picks him apart with greater accuracy and sharp quick counter punching. Vitali style wasn't suited against guys who had longer reaches and stood just as tall. Lewis was past best , slow as a sloth but was able to land so cleanly , he made Vits face look like a butchers bin after only 6 rounds. AJ can do what Lewis did , and more.