Webber was more athletic but was never really a high flyer, more of a power dunker, Cousins is more than capable of throwing down some power dunks. Skill wise they are very similar though, both have vacuums for hands, great handle for big men, passing, mid range jumpers and both Webber like Cousins is solid in the post but not great(Webb never really had an array of moves other than a half hook, like current Cousins, although he is starting to show more and has time to improve).
I didn't see much of Malone, but from what I have seen he reminds me more of a more skilled Blake Griffin.