The finale of Season 2 has what is probably one of the most heartwarming moments of the entire series, especially considering the relationship between the two characters. Gareth Thomas's delivery clinches it.
Blake: Avon. For what it is worth, I have always trusted you. From the very beginning.
In "City at the Edge of the World" Vila — the most despised and disparaged member of their group — is sent down to the planet and then goes missing. After finding out that Tarrant intimidated him into the job the entire crew goes down to rescue him. They get really nasty when threatening his captor, and throughout it they appear to have no other motivation than "we want our thief back".
Avon, in his own inimitable way, defending Cally when some of the other crewmembers indulge in some Fantastic Racism.
"She's more human than I am."
Dayna and Cally's response to Avon when they decide they are going to accompany him on an extremely dangerous mission to help him get his revenge.
Avon: "This has nothing to do you with you."
Dayna: "But you have something to do with us."
Cally: "Yes, we talked it over and decided we care what happens to you."