I voted Dantonio then looked at Purdue's past. Tiller turned a long term disaster into a good program. MSu has always been ok.
FWIW, in 1973 Purdue lured away Northwestern's coach who was coming off a 2-9 season.
Yep. They're both great coaches, but in my opinion what Tiller did at Purdue was the far more impressive feat than what Dantonio has done at Michigan State. You have to remember the true football wasteland that is Purdue, how its locale, its tradition, and overall interest in its program are all very much lacking in comparison to MSU, and how other than that very brief glimpse of glory behind QB Mark Hermann and under Hall of Fame coach Jim Young in the very late 1970's, Purdue football had been a chronic loser for the better part of three decades prior to Tiller's arrival. What he did at Purdue was similar to what Bill Snyder did at K-State in that both somehow resuscitated what had been a corpse, and the longer Tiller's been gone, the more you realize how what he accomplished there was such an aberration, as since his departure, Purdue has retreated right to the same doldrums it had been inhabiting prior to his arrival. After Young left in 1981 for West Point, Leon Burtnett, Fred Akers, and Jim Colletto posted a collective 54-107-5 record at Purdue, then Tiller came in, coached 12 seasons while leading them to 10 of their 16 all time bowl appearances while posting an 87-62 mark, then he retired and Danny Hope and Darrell Hazell have subsequently gone 42-57. The common denominator in both Tiller's predecessors and successors is that they have all found that it is an exceptionally difficult task to win at Purdue.
He was a true innovator too, as he was the first coach to introduce the spread offense to the stodgy and hidebound Big Ten. Everyone was doubting that audacious approach, and I remember Lloyd Carr and many others derisively dismissing the thought that anyone could win playing pitch and catch football in the cold-weather Big Ten. Tiller enjoyed all those doubters, and he'd chuckle at the lot of them while saying "Just wait and see.", and see they did. He was a really cool guy and a great football coach.
Sparty on the other hand, well, they were mostly just mediocre at worst prior to Dantonio's arrival rather than truly wretched as Purdue was prior to Tiller. There were the Saban years of course at Michigan State, but even prior to him George Perles put up some very quality seasons (including the 1987 Rose Bowl) at MSU. It was never so much that Michigan State was truly awful, but just that for a long time they were very much the little brother to Michigan when that program was at its peak, but now that worm has turned completely.
Anyhow, very long story short (and my apologies for rambling), what Tiller did for Purdue was borderline miraculous, so my regard for his coaching abilities could not possibly be higher.