An author of a novel is not necessarily the narrator of that novel. In this case, the author of My Ántonia, Willa Cather, is different from the narrator, who is a fictional character named Jim Burden. Jim does admire Ántonia Shimerda. They both grew up poor on the plains of Nebraska, where they had many adventures out on the land together and became good friends. While there are numerous characteristics of Ántonia's that Jim admires, three main ones are her honesty, her vitality, and her kindness.
Ántonia can be said to represent to Jim all that is good and simple about his childhood before he moved to the East Coast to become a lawyer. Ántonia is linked to a simple, pure, and basic way of living on the land, where deep feeling and experience occur. As a character, Ántonia is full of life, expressive, and outgoing. She has an easy time making friends and children love her—for a while, she was a nanny. Jim likely admires these traits in Ántonia because he is a more reserved, scholarly person and does not express his joy or feelings as fluidly.
Life takes a hard turn for Ántonia in the sense that she has some difficult experiences, such as being sexually assaulted by her employer while she is a nanny, and later in life, a man she falls in love with abandons her while she is pregnant. Her life takes a different path than Jim's; he goes on to make a good career for himself as a lawyer. Ántonia goes on to have ten children with a farmer and remains poor in Nebraska. But her kindness and openness never change, and because of this, Jim holds her in high esteem his entire life. The fact that the title of the book is "My" Ántonia indicates she is as dear to him as his childhood itself. To conclude, Jim, the narrator, admires Antonia's honesty because she is expressive and open; her vitality because she has the rustic, rugged qualities of being a farmer in tune with nature; and her kindness because she has a good heart and moral motivations.