Seth Rollins by far, especially in 2014 when he was a heel and he had the feud with Lesnar and when he feuded with Ambrose leading up to the lumberjack match which was, shock horror, interesting and different from what they usually do.
He's the best in-ring, the best seller without looking stupid (see Ambrose), can get by with his mic skills and doesn't say cringeworthy things often (see Reigns), a great heel, not so sure on him as a baby face and has the most memorable moments in the last 3 years, for all the right reasons.
Maybe Reigns is bigger and Ambrose is better on the mic but overall, Rollins is the best overall. I just wish he would just stop changing his finish and develop some more dimensions as a baby face other than "I came back from injury and I'm sorry for breaking up the shield".