Joshua has the bigger star potential no doubt, Fury is probably about as high as he can get especially considering his religious views.
I think Fury would beat them all at the moment because for a big lumbering awkward guy he can move fairly well around a ring. Both Wilder and Joshua have tremendous power at their disposal but they have to land it. Wilder is faster in athletic terms than Joshua and he looks more mobile whilst Joshua I could see having trouble catching up to Fury.
As for Wilder vs. Joshua I think unless Wilder stays really mobile he'll end up in a slugging match and I think Joshua can take a better shot and has the better boxing fundamentals. That's just imho