#1 Aleister Black
Well, this may be an answer that could shock many, but I did say "surprising" entrants who could win.
Now, the rumor is that Aleister Black will challenge Andrade Cien Almas for the NXT Championship on the TakeOver the night before WrestleMania - and, with one defeat that didn't see Black submit or be pinned, you'd have to make his favorite.
This may not be the case as it's only a rumor right now, but even if it does happen, I think there are two routes WWE could go to introduce Aleister Black to the masses.
Either he comes in and wins as NXT Champion, and either goes back to NXT or relinquishes the belt to compete on the main roster.
Or, and this one might be unpopular, loses to Almas at TakeOver New Orleans and enters the Battle Royal on a rampage, destroying everything and everyone in sight.
Either way, Black is one of the most over and Superstars in WWE right now and is, deservedly, receiving a monster push. Don't be shocked to see Black either as top dog in NXT or on the main roster after WrestleMania.