These are the two videos that convinced me.
https://www.youtube.com/watch?v=cvGn1WgYQSQ
https://www.youtube.com/watch?v=NkPc4SZS5Ok
While I think that Levis has the most upside, I see to many Wentzism's to ever believe that he will get there.
Stroud has room to grow as well, but I believe that he is closer to his ceiling and his ceiling will be very very good.