#6 Dolph Ziggler
One thing which NJPW wrestlers do way better than the WWE Superstars is "selling." They make simple moves like dropkicks and clothesline so devastatingly painful. But in the WWE, most of the wrestlers react to it as if nothing ever happened.
However, there is one Superstar who does it better than his counterparts, and his name is Dolph Ziggler. Dolph has been praised repeatedly by the Internet Wrestling Community for the same, and he only gets better with time. However, the WWE uses him as a gatekeeper. He is only called when required to give a "push" and then goes back to obscurity.
If he goes to NJPW, they won't treat him like that. He can be a legitimate threat to Jay White's United States Championship and used in the title scenario. He might even become the first American to win the IWGP United States Championship; who knows?