My personal favorite is Dillashaw Vs Barao 1. I was in awe, I couldn't believe what I was seeing. The footwork, the feints, the combos, stance switching. TJ put on a masterful performance the night he became champ.
My two runner ups to round off my top 3 are Lawler Vs McDonald ll and Max Holloway Vs Cub Swanson.
I know most of the fights are from more recent years, and that's because in my opinion the focus on technique over toughness has made MMA more enjoyable. I do enjoy my Melendez Vs Sanchez and Shogun Hendo here and there, but for the most part I've been more into technical back and forth wars.
Lyoto Vs Thiago Silva is also up there. First MMA fight I ever watched. Made me an instant fan of Machida.