Chill guys, lets get back to the topic.
Well, I personally think Mace is greater. Well obviously to be the creator of any functional form one has to be the master of at least one form, and deep understanding of styles and xp on what "other" people out there would use.
Vapaad is an extremely hard form to even learn, not to mention master, and one can only imagine its difficulty of creation. It takes intense training to even try to learn the form, or else. Remember many Vapaad wielders turn to the dark side. Sure its an "enhanced verson" of some pre-existing forms if you might call that, but what isn't? Most things are built on understanding of the old.
However, even master have different grades and levels. Obi is definitely on the high end of Mastery. Though I am sure learning and training in Soresu is definitely easier, relatively.