The best.
The way Crocodile came together as a villain, along with his arc, is nothing short of a masterpiece. This was our first major antagonist, one which every proceeding one would be measured to. Crocodile was a looming presence the moment the Strawhats entered the Grandline. It would build and build as we learned more about his organization, and coming to a head during Alabasta. His plans, design, demeanor, were all top notch, and he presented himself as Luffy first true challenge. One he would continuously lose t until he narrowly defeated him. The anime playing Symphony no. 9 was cherry ontop in making Crocodile's fall that much more grandiose.
His return in Marineford was great for how it further cemented his character outside of being a villain, and I am more than interested in seeing where he goes now that he's regained his spirit as a pirate.
Teach and Akainu are up there largely for their build up. Depending on how it goes with them, they may surpass Crocodile.