Most bands that would qualify for this are bands that have been well covered by official releases. Like for instance there was a time when a Grateful Dead bootleg probably would have been their best. But now tons of that stuff has been given official release so it doesn't count as bootlegs anymore.

Ditto for The Who. For years the only live Who album available was the 6-track Live At Leeds. and then some 80s live albums. During that time Who bootlegs would have definitely been the band's best. But in the 90s Isle of Wight and the expanded Leeds came out and more archival releases have followed.