I'm going with Ainge. Drafted the Jays, Smart, Rob, PP and Grant, hired Stevens and then was the one who introduced him to Horford and Theis. Without Ainge, we have potentially no stars, no DPOY, no super-vet and no Stevens.
Stevens obviously deserves some credit though. He hired Ime, made a gutsy trade to send out a first to get Al back, and brought in D-White.