Roku - his avatar mastery feat is all I need. But he has good feats in the Reckoning of Roku novel.

Korra - best showings of skill in firebending of any avatar. can use fire jets and sustain large blasts

Wan - pioneered firebending and should be very skilled with it

Aang - natural talent and quick study

Kyoshi - I don't actually know much someone else help me out