What are the best exercise routines for MMA take downs?

Since your question is based on takedowns in general and not a specific type of takedown (ie. slam, drag down, push down..), a good routine could follow grip and squeeze pressure (we don’t want them breaking loose in mid takedown) as well as back extention and leg strength. A lot of fighters here practice push/pull methods to deliver more force than can be generated from a stand still. The MOST important factors in takedowns are commitment and follow through so, plyometric exercises could also provide a good basis for muscle memory (you know, like instinct). Good luck!