Leach will make MSU an air raid no defense team and will light up defenses with 2 star qbs that no one in the P5 thought should start for 3-4 years, but will give up tons of points
Kiffin will build a solid offense with a decent by ole miss standards defense. If he gets a great TE then he will be tough to stop. I think Kiffin has better staying power if he beats MSU and stays out of trouble.
Ultimately I see Kiffin as a 7-9 win coach at MSU and Leach as a 4-7 win coach (lower number worst case and higher number as best case). But ultimately their tenures will be decided by the Egg Bowl and Bowl games. If Arkansas becomes relevant then all bets are off.