For simplicity it's best to divide Mitchell's work into three relatively distinct periods: the folkie, the jazzy years and the Larry Klein years. Her vocal artistry is the constant element throughout. "Blue" is generally considered the peak of the folkie period. A lot of people like "Court and Spark", but I prefer "Hejira" for the jazz period. The Larry Klein years is something of an extension of the jazz period, but the overall tone is more mature and relaxed. Try "Night Ride Home" or "Chalk Mark In A Rain Storm".
Mitchell always surrounds herself with first rate musicians (Jaco, Tom Scott, Larry Carlton, Pat Methenay, Joe Sample etc.) and sonically the albums are high quality studio multi-track, but not audiophile recordings.