Sherman by a wide margin. Sumlin MAYBE was a better gameday coach, MAYBE, and for sure is a better college oriented coach, though you wouldn't know if from the last 4 years.
It was obvious in mid-2015 and only became more obvious. The further we got away from Sherman evaluated, recruited and developed players the worse the team got.
Sumlin's recruiting was actually never that great. Sure, Kirk and Garrett were day 1 NFL ready guys, but RB recruiting was almost a total failure, LB not much better.
Development? Sherman evaluated, recruited, and developed Sean Porter, Jonathan Steward, Ryan Swope, Nemo Hicks, Mike Evans. Mike Evans was in Sumlin's back yard at Cougar High and he didn't recruit him, Sherman did and knew he could be an NFL WR.
Sumlin recruited guys that dominated a HS game, then they came to A&M and never got better. RSJ was no better when he left than the day he showed up.
Sherman took over a disaster of a roster, and left a team with top 10 talent on offense 2-deep and good starting defense, but he never did get enough of depth on D though that was building.
Under Sumlin, after everything he inherited and took over both on the field and the facilities provided, in Year 6 we were tied 14-14 with a IAA FCS school in 4Q. That is just abysmal. Yeah I know Sherman lost to Arkansas State in Year 1 and Sumlin didn't lose to the FCS team Jax State, but Sherman inherited a poor roster.... Saban lost to ULM (or ULL) his first season in Tuscaloosa.
The biggest failing of Sherman was he was too much of an NFL guy and called the game as an NFL game. In the NFL if you have 14 point lead and the ball but there is 4 minutes left, that game is in doubt, you have to close it out. Even the inept Browns can get a stop or turnover on any play and score quickly. In college, if you have a 10 point lead with 5 minutes left and you have the ball, it is very difficult to lose that game if you run the ball a few times and get just 1 first down. But Sherman would operate the O like it was the NFL and that is what led to several of the 2nd half blown leads and losses in 2011 primarily due to ill timed Tannehill interceptions. Conditioning was fine in 2011, as evidenced that we were such a strong 2nd half team in 2010.
Sumlin will always be the coach of record for 2012, but the last 3-4 years is the real Kevin Sumlin Aggie football. He never could have built and developed a team like 2012.
I for one do think Johnny would have been the QB in 2012 under Sherman, he was just so dominant on the practice field and made so many dynamic plays. But even if he wasn't.... granted no Heisman and likely loss to Bama, but we would have beaten FL and maybe LSU and all those other games would have been the same result. We killed State, Auburn, Mizzou as our OL was dominant and D was solid, and we wouldn't have had SIX turnovers vs. Ole Miss.
Sherman every day of the week and 10x on Sundays. Sherman won NFL division titles, he built the A&M program Sumlin developed, Sherman had a tough team. Sumlin only TALKED about being tough and has never won anything.
We have a REAL football coach now, who is laying down excellent recruiting of real football players who can play, compete, and win in the SEC, and he is focused on being tougher and winning at the LOS. Sumlin could have been here another 10 years and would have gone 0-20 vs. Bama and LSU as his vision of college football does not win big games against tough teams, and quite simply Sumlin could not evaluate and develop talent very well.