User blog comment:Red Eyed Raven/dynamic duos/@comment-5962458-20131119085928

Well, Shanks and Mihawk came first in mind. Those dudez are so strong that fight each other casually in order to keep up in shape, since there is no other serious rival for them.

As for a future relationship, I'd like to see the one between Luffy and Smoker growing into a Roger-Garp-like one.