I think Gordon can turn into an excellent player. I do think Wiggins is the better prospect though but it would not surprise me if Gordon turned out to be a better player at some point. He just NEEDS to improve that shot. His form is awful. He seems like he has the drive to get better though.
For the record Im not very high on Wiggins. I think he could be a nice player, multi all star and nice career, but not a superstar. Just my 2 cents.
So in summary, Wiggins is closer to a finished product than Gordon, but Gordon has the tools in place (minus shooting).