Red Mitchell is pretty much my all time favorite straight jazz player. He is a model of creativity for any artist. Even though he did make a few avant garde lps (Ornette's first, and with George Russell and a Max Roach Lp with Steve Lacy) what is most striking about him to me is that he just pushed straight playing right up to the edges without going "out".
He used interesting re-harmonizations, asymetrical bars of soloing (esp. in duo, for example Red solos for 7 bars, Warne marsh for 3, Red for 9 and so on keeping the form all the while) and many other creative devices.
He was also technically amazing, with great facility through all registers both Pizz and arco.
He was also teacher to some amazing players like Lafaro, Peacock and Dresser.
Both my favorite straight ahead lp and Favorite Red Mitchell Lp is "I Concentrate on You" duo with Lee Konitz.