Too early to tell. Fury's been improving, and trying to put a few Klitschko-esque wrinkles in his game from what I've seen of him. Wilder has nearly identical reach and can at least match his power.
Pajkic, a guy with a KO percentage of 29% against mostly nobodies, sent Fury down hard. Wilder has fought even worse competition, but has a massive punch and has stopped every opponent thus far.
I'd lean towards Fury simply because he's been in there with some better opponents, but they're both still young and crude as hell. Wilder could easily put Fury away in a few rounds (and vice versa).
Shame we won't see this fight anytime soon.