I used to use Prime Nesta but he causes so many unnecessary penalty and too slow to react at most dangerous situation.
I use all my untradable cards and Nesta for this Capitano Fabio Cannavaro, the golden ball winner 2006.
He is too good at defending, strong, giant leap and powerful heading. Surprisingly, he can outjump the dangerous target striker such as Zlatan Flashback and CR7. He's the cleanest tackler among all my defender. Since i use him, i never concede any penalty yet.
The best of the best... don't judge the book by the cover... i mean don't judge him bad because of his height, his jumping and heading are monster.
-His defensive ability is like Kante + Sergio Ramos combine
-Jumping + heading
-Positioning to block opponent shooting