Kizaru, Akainu, Aokiji, Sengoku and Crocodile come to mind
If I'm to choose one it is probably Akainu. He has all the characteristics that make him a ruthless man, but behind this attitude is a noble cause, making him by default a self contradicting character. His character will be fleshed out more later on but the basis for such claim can be made from what we know.
Dragon will also be a pretty good character seeing how Oda handled him so far, unironically