I feel like Stevenson is the tougher fight for the 1st half, and Kovalev is the tougher fight in the 2nd half.
Ward is more skilled and quicker than both, but the quickness/speed gap isn't as wide against Superman. Both have great lefts, but Dre uses his right more effectively and its it's own weapon whereas Adonis mostly uses it for setting up the left or body punches. His lack of combos and punch variety is his biggest flaw, but it also fuels his biggest strength, which is that monster left that he knows how to set up so well to crack everybody with. He'll sell out with it early in hopes of getting you out of there or discouraging you from trying too hard. It's like a chain reaction because that causes him to gas out a little for the later rounds. Seen that against Fonfara. Ward can figure all that out no doubt, the question is can he do that without taking too much damage in order to sweep the 2nd half and win.
Kovalev is more patient with his impending aggression. I see him turning it up more late and being able to hang tough longer. That demonic final round against Hopkins is an example. Dude turned into a SNK boss during that round. Ward needs to dominate them early and middle rounds in case he has to dig deep and survive something big from Kovalev late in the fight.
With all that said, I'd still favor Ward to beat both.
I just think if he has any shaky or rough patches in those fights, they'd come early against Stevenson and late against Kovalev.