#4 Tetsuya Naito
Naito has an advantage over a lot of the other Japanese wrestlers in NJPW - he has a distinct and popular character.
Tomohiro Ishii and Hirooki Goto are great also, but Naito has an attitude that translates to any country or promotion.
Naito went from being a white-meat babyface to the cocky and 'tranquilo' version of the superstar we see today. Naito has parlayed the success he's had with Los Ingobernables de Japon into becoming one of the top three Japanese draws in NJPW along with Hiroshi Tanahashi and Kazuchika Okada.
Okada is an amazing wrestler, but he's well behind Naito when it comes to personality. If WWE did sign Okada, he'd be relegated to Hideo Itami status - great wrestler with no discernible character other than great at wrestling.
The best thing for Naito was wrestling with La Sombra (now Andrade Almas) and forming a Japanese faction of LIJ. You could even say their popularity rivals that of the Bullet Club in NJPW and ROH.
Naito would be a great addition to WWE but he might suffer the same fate as Shinsuke Nakamura. Both are amazing in the ring but might fall victim to WWE's reluctance to book Japanese wrestlers as world champions.