From a pure conceptual perspective, which is the better "Gimmick controller", Wii U Gamepad, or Joy-Con?

[Jumpin]

I also wouldn’t really call either a gimmick. A gimmick is something like “blast processing” or “New tropical blue colour.” Basically a novelty attribute with no substantial purpose other than generating interest: while Wii U’s Gamepad and the Joy Cons clearly have interface applications of substance - regardless of how you feel about them.