I listen Live At Leeds. Fuck! It's pure fucking rock. Good rock. I listen Live At Japan by Deep Purple. But ... Fuck, Live At Leeds rocks the fucking World.
On most good live albums, there is either some sort of improvisation or it's just an exceptional performance that captures a certain sort of energy. I can't really answer it better, I kind of feel the same way about live albums (that aren't jazz or jam or w/e), because if all they are playing is the studio songs as they were recorded, what's the point?
This album is severely underrated
Also, if you count Sister Ray as live, it's the best live song.
Live at Leeds has quite a lot of jamming, especially Heaven and Hell, Young Man Blues, My Generation, etc...
But I assume the Grateful Dead would exceed that jamming by a huge margin.