Well it depends partly on how you define success in the wrestling business. If we're going off the idea that the bigger the draw, the more successful the career, than undoubtedly we'd have to give the nod DiBiase here. As great as Tully and the rest of the Crockett crew were, they were never big draws, atleast not compared to the crowds the WWF was getting at the time. DiBiase definitely wins in that regard.
If we're talking about who was better at what they did...well that's arguable. DiBiase was absolute gold on the microphone, but Tully was no slouch either. I'd give Tully the nod over Ted if we're judging in-ring skills. Legacy and importance...again you'd have to go with DiBiase, simply because of his time in the WWF.
These are two of the most underrated workers of their era, so this is a rather difficult decision for me to make. For me to choose my personal favorite...again, very difficult. I love both of them. DiBiase, next to Roddy Piper, was the most underrated heel of his era. Tully though...man I might just go as far as to say he was my favorite member of the Four Horsemen. He was the true worker of that group.
I'll give the nod to Tully, only slightly. Both are legends and were absolutely wonderful at what they did. For those unfamiliar with Tully and his work in the NWA...please, turn off The Price is Raw, and go watch the old Starrcade shows from the 80s, immediately.