I would go with Maskaev due to the fact that he had been Ko'd by weaker punchers than Vlad. Sultan is totally untested against strong opposition, so I cannot make the right judgement there, even though he had been KD by lesser punchers as well.
Anyone picking Wlad is picking out of hate or ignorance. Not that he has a great chin, but Maskaev has been starched for a 10 count on at least two occasions and stopped 5 times over all, Wlad has been stopped fewer times in more fights, and has never been stretched for a 10 count, and Maskaev has been stopped in 4 rounds or less 3 times
Wlad and Maskaev are chinny but they can fight. Maskaev's turn a round is amazing? Maskaev is live against Peter if Peter comes in out of shape. Oleg has become a savvy old pro.
Chagaev hasn't even been knocked down to my knowledge so he gets a pass. Sultan has only had off balance type knock downs, so he gets a pass too. Wlad has only lost due to once due to punches rather than fatigue. He's never been "starched" or counted out. Even though he's faced far better competition than Chagaev & Ibragimov he gets my 3rd spot. Maskaev has been overwhelmed & beaten to the punch & KO'd for the count. He has the worst chin here but Oleg has grown a bit savvy & I don't think Peter is all that. I'd be surprised if Maskaev is KO'd early and that's saying a lot.
Maskaev. It's not even close. Wlad has been down, but he's never been knocked out cold like Oleg - the classic sign of a glass jaw. He's gonna get creamed by Peter, too.