#1 Karrion Kross
This selection is the most obvious one since it's been hinted at ever since Karrion Kross squashed Tommaso Ciampa. Kross had Scarlett deliver an hourglass to Adam Cole to signify that his time atop NXT was running out. Keith Lee eventually destroyed that same hourglass backstage.
With Cole out of power and Lee now the top dog in NXT, Kross will clearly still target The Limitless One (or whoever holds the gold). Even after Lee was victorious last week, one of the last shots we saw was of Kross and Scarlett peering down at the ring at the new double-champion. The Tollman of NXT is aiming for Lee and the match could come to fruition sooner rather than later.
While I think Kross should be the man to eventually dethrone Lee, it seems like that would be too soon. Lee just won the major title in NXT and needs a lengthy run to prove it was the right call. Kross winning the title would make me happy but it may be too soon for the two to square off for the NXT Championship.
Think about how Bray Wyatt and Braun Strowman immediately squared off for the Universal Championship following WrestleMania 36. It was too soon so Bray Wyatt, and not The Fiend, was the one to face Strowman at Money in the Bank.
Kross was a huge free agent signing and needs to be treated like the big deal that he is. His act with Scarlett is truly unique and his aura is special. Whenever it happens, Kross and Lee are facing off for the NXT Championship and it will be awesome.