I would say Wlad losing a fight. Both are highly athletic and around the same Age and didnt really slow down so far. But i realized that Wlad started to get hit a bit more in his last fights. As bad as Haye performed against Wlad, he landed a bomb in the 12th Round and Wlad was hurt, he did everything right to recover this time but his chin is still weak. He got rocked by Wach who might have the slowest hands ive seen in a recent HW title contender. Pianeta came through with some sloppy hooks too. And there is a new generation of hard hitting big HWs on their way. Floyd showed us against Guerrero that his legs arent shot as people made it out to be and didnt get hit with clean shots the whole fight. And even if he gets hit we saw that he can take a good punch and has good recovery skills (Mosley).
It didn't appear to me that Wlad was getting hit more, but I haven't checked the stats compared to previous fights....he could be. Although it's important to note that Wladimir has also been much more aggressive in his last few fights, which naturally opens up a fighter to be hit more. No, Wlad was not "rocked" by Wach....watch the slo mo replay, Wach got one hit in, Wlad's eyes were clear, and he slipped all of the other punches in the flurry by Wach.
There is no elite fighter in Wladimirs division except his brother. Floyd could face an elite fighter. But Floyd is the much better fighter than Wladimir. So it makes it even.
Maybe no elite fighters but there are some guys who could give Wlad problems. Kubrat Pulev is very underrated, he has good size (6-4) and reach and a solid Jab. Deontay Wilder might be untested but he is actually bigger than Wlad and has a great punch and a 84 inch reach.
Floyd will never take a fight which he might lose. Never. And he's very good at being consistant and winning the fights he's supposed too. SO i'll pick wlad. He's still chinny, and theres some great prospects coming through the ranks.
Wlad is more likely to get floored by a lucky punch than Mayweather. This is boxing, shots out of nowhere have changed history. Keep in mind "more likely" is about a 2% shot to Mayweather's .2%.
Although Floyd is a shark himself, he is swimming with other sharks. Canelo, Trout, Lara, Garcia, Matthysse, Alexander. Wladimir Klitschko is an Orca swimming with sea lions and penguins.
Wilder has said sparring Wlad was "very humbling", he admitted he has his "work cut out for him over the next couple of years". Wilder is no match for Wlad.
All Wlad has to do is line em up and hold them to death, like he always does. Floyd is fighting people with talent that does not exist in the HW division.
Even though Floyd cherrypicks the hell out of his opponents, Wladimir is less likely to lose. He has no real threats. Povetkin went life and death with Huck. Fury is chinny as hell and crude. Abdusalamov has no defense except his offense. Pulev is decent but not enough to beat Wlad. Gonna be a nice, easy ride into the sunset for Wlad.