#1 Frankie Kazarian

Fans may be blinking their eyes at seeing Frankie Kazarian at the top of this list, but the current AEW star wrestled for WWE in 2005. Kazarian was introduced on Velocity at the height of the Ruthless Aggression Era as "The Future" Frankie Kazarian. He spent only a couple of months with the company and was 'undefeated.'
Kazarian attributed the briefness of his time in WWE to him not being mentally prepared and said:
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"I couldn't do it mentally. I don't think I was mature enough and there's an awful lot you have to take in when you get to the WWE."
Kazarian would eventually become a big part of Impact Wrestling/TNA for several years and then spent some time in ROH. His association with Christopher Daniels and Scorpio Sky as SCU has proved to be a hit across several promotions. He even ended up becoming one half of the very first AEW Tag Team Champions, alongside Sky.
It'll be interesting how his career shapes up in AEW, but considering his past successes, it wouldn't be surprising if he continues to impress fans even more down the line.