Dang I dunno... I guess I have to go with Thurman based on better experience and opposition. Wouldn't be surprised if Spence managed to win a close 10 rd decision.
I think Spence.. a lot of people say he's fought nobody but Lartey for example would beat most of the fighters Thurman has fought.
He's fighting Roberto Garcia next I believe? That fight will answer a few questions I have about him.