The best live band I ever saw was unquestionably Leonard Cohen. It was a year or two before he died. It is hard to say what was so good about him, but he really was.The second best was probably Chic, seriously, those old soul bands are fantastic live. There were some good bands at the first WOMAD festival, and also at the Notting hill carnival (but that was a long time ago. The last time I went to Noting hill it was terrible. Not even any music that I saw. Just crowds and piles of food packaging in overflowing bins). I think King Sunny Ada was good. The Blockheads were good, so was Uriah Heep (although I could not understand any of the words).
Some of the best live music I'v heard was played by obscure little blues or jazz bands. I almost forgot, The Blues band at Glastonbury. I think it was 1981 or 82. I am stopping now. This is just making me feel old.