#1 Asuka

I'll admit that this one is a bit of a cop-out because the recently called-up Asuka is technically already on a 510-day undefeated streak, as she was unbeaten during her NXT Women's Championship run.
However, "The Empress of Tomorrow" has only been on the main roster for two weeks and is currently 2-0, having beaten Emma at TLC 2017 and again on the following Monday Night Raw, meaning that we're still early days into her main roster run.
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I see absolutely no reason why the WWE would need to deviate from the norm with Asuka and have her lose a match anytime soon, even by disqualification or count-out. If they want her to be as big of a star as she clearly can be, they need to keep her undefeated streak going for as long as they possibly can.