For me, I think Ambrose. He has the mic skills and is a great wrestler. I see him in the Upper-Midcard or Main Event fighting for major titles, most likely when Cena is done.
Rollins is second. He is amazing in the ring and has potential. I see him in the Mid-Card fighting for the I.C. and U.S. title. Maybe being champion soon.
Reigns would be third. He does have the look in WWE and has a great Spear. I also see him Mid-Card(Maybe Upper-MidCard) fighting for the I.C title.
Conclusion, Ambrose, Rollins, Reigns