My perspective is a little different on this one. At this point until they fight, if they even fight, we won't know who's the better man. Regardless, Thurman has paid his dues, and is probably the most deserving of a big money fight. The only other two dudes who I think are as equally deserving are, Timothy Bradley, Kell Brook, and maybe Porter (had he not lost to Brook, lord only knows how high his stock would have been). Everyone else in my opinion, including Spence, needs to pay their dues. I think it's borderline disrespectful to Thurman to think he's obligated to fight Spence. No, Spence has to pay his dues like everyone else. If anything, Spence thinking he deserves a fight with Thurman, is almost tantamount to Khan's delusional azz thinking Floyd's legacy will be diminished if that fight doesn't happen.
I think the most reasonable fight for Spence would be Porter. Regardless, it's going to be interesting watching Spence's career.