Seems like this might be anyone's guess as to who might win. Though even though I'm more of a Wario fan i think Dedede takes the win.
Speed: Dedede definitely takes the category because he can keep with the warp star which has shown to travel at the speed of light. Also he has mobility thanks to his ability to fly like Kirby too. While Dedede is techincally slow on the ground like Wario because of the fact he carries that hammer on him at all times, he still takes the speed category because of this feat. Wario is fast given the Wario bike, but no where close to Dedede.
Strength: Wario wins. Wario has been shown to lift pyramids, break through metal like it's paper via shoulder bash, has strength rivaling that of Donkey Kong and Bowser, benched both a T-Rex and King Bomb who has been recorded to weigh over 34 tons. Dedede does have some good feats like being to hold up a monster that crashed through his castle, can break through stone, rock, and even metal, but he needs his hammer in order to do it whereas Wario only needs his his bare hands.
Durability: Seems pretty even for both opponents. Wario's body is pretty malleleable to the point where it is toonforce level to the point it's ridiclous. From being set on fire, turned into a zombie and vampire, being crushed, twisted, electrocuted without even a scratch being left on him, and survived the dispersion of a cloud from the Shake King. Dedede has taken constant beatings from Kirby who is said to be planet level, survived being stuck by lightning, having a house fall on him, survived being dipped into the sun, being shot out of a cannon and going through rock, had his stomach torn open when possessed by Dark Matter, been hit by a barrage of lasers, etc.
My biggest concern for Dedede comes from the fact that some feats of his are accomplished via scaling. I think one example might be the explosion that Kirby tanked at the end of Triple Deluxe. Just because Kirby survived the explosion with no damage doesn't mean that Dedede scales to Kirby just because he can keep up with Dedede.
But who knows. As long as we don't get another Zelda vs Peach, Shadow vs Mewtwo, Yang vs Tifa, Garra vs Toph, or Scout vs Tracer I'll be happy with the results.
