The ultimate bender that is. And for more reasons than her supreme ability to waterbend, including its other categories to perfection. First off, her caring and nurturing nature made her like a mother figure not just for Aang, but for the rest of Team Avatar, allowing herself to be a shoulder to cry on. Her selfless service in the face of adversity went far and beyond the norm for anyone. Strong and courageous at times, she was literally the glue that held the team together. She is extremely overprotective, especailly when it came to Aang.
In my opinion I do consider her to be on par with the Avatar, since it was her, that rescued and saved Aang's life twice, if I recall......once from the iceberg and the second time from his battle with Azula, Zuko, and the Dai Li. Her spirit, was the only one that held the Avatar in place on the earthly plane of existence, had he died fully, no more Avatars. She too, also cotrlled Aang's raging avatar state on more than 2 ocassions. Katara is much more than just a simple bender....she's a healer, a warrior, a counselor, protection, a teacher, a life saver, and most imortantly, a mom.