There isn't any question The Allman Bros. Band is and always will be the best Southern rock band.
Mickey Hart and Bill Kreutzman were pretty seamless themselves too.
Duane was among the best of the best for sure. I followed their music thru the years and have seen them many times. Not always a great show but had a good time either way. Greg knows his stuff too.
Steve Miller? people don't even know what he looks like
he used to ride a bicycle around the parking lots before concerts because he was not recognized. I would not classify his music as southern rock, it's nowhere near that, more like some kind of poprock.