Jam bands with the best singers.

So I love Jam bands, but I notice that sometimes they don’t have the most skilled singers. I love Jam bands for the groovy, funky, and experimental instrumentals and absolutely love the musicianship but when I listen a lot of some very highly regarded and famous jam bands, well the singing is just a little off par. What Jam bands do you think have the most talented singers. Also if you agree with me who do you think are the worst (not to make fun of anyone though)