Sullinger in my opinion, and it's not even close.
We know what we are getting with Thomas, Bradley, Turner, and Bass. Sullinger is in his third year now, and had he not been injured he would be a key cog in this team. This guy can ball, eat the glass, score on the block, and is a high IQ player, and we have seen it for 3 years putting his injuries aside. Conditioning will be a huge factor obviously along with getting back into rhythm, but on the offensive end he has an advantage if he is matched up with Love or a small ball team with Marion or something at the 4.
Also, he has had some huge games for us in the past so we know he can produce.