Let's be serious people, the fighters that has the best takedown defense in MMA history and whom perfected and popularized the sprawl-and-brawl technique which is part of it:
1) Chuck Liddell (Couture is the only one who was able to take Chuck down at will and keep him down, watch their 1st fight).
2) GSP (Kosheck is by far the only fighter who took GSP down couple of times, watch both of their fights).
3) Cro Cop (remember people, Mirko was fighting guys twice his size, so that says it all).
4) BJ Penn (he's not even a wrestler, and was also fightin guys way bigger than him, and they still had problems to take him down, watch his 1st fight with GSP, 2nd fight with Hughes).
5) Lyoto Machida (also not even a wrestler, BARELY got taken down in his whole mma career, only got takin down once by Jones and Rampage).
6) Junior Dos Santos (fought some of the best in the HW as Roy Nelson, Shane Carwin, Cain Velazquez, and still didn't got taken down at all).
7) Rashad Evans ( BARELY got takin down in his whole mma career too, only got takin down a few times by Tito Ortiz in their 1st fight).
Honorable mentions: Kosheck, Sherk, Rampage, Matt Hughes, Thiago Alves