AdBlock+ has an automatic whitelist when installed that allows certain advertisers through the blocking mechanism. The fact that these advertisers pay for this privilege makes this particular scenario rife with conflict of interest.
When using Greenify without ROOT access to hibernate apps, it has to be done manually each time. There is a widget and shortcut that users can set to their home screen to make this action a bit easier though.
Xposed can radically modify the behavior and look of the system and apps without having to modify any APKs. This means that Xposed modules can work with different versions of the same ROM or even different ROMs altogether.