The reason why I say this is because this the album, alone, that would make her the Queen of Soul. I never bought that "Empress" title and realize that another notable may not be in the best of health as I type. That understood, I will never change my mind on how awesome this album is...the vocals, arrangements, everything. So while there are many tracks to fall in love with (and I'm not a fan, btw), I'm going with the title track though I don't know where this performance took place.
My other choice is also not 100% personal. Though I love Sly and the Family Stone, my knowledge of Larry Graham was limited until he opened for Prince back in 1997. Let's just say I couldn't wait for the main attraction. People ask me to this day if he sang his 1980 hit 'One in a Million' and I say no, it was like a Sly Stone concert with no Sly and a loud guitar.
However, there was this one song I couldn't get out of my head growing up. Never knew who sang it and it was one of the few my mom hated (because she pretty much had a record store...we lived down the street from a VIP Records, btw). So anyway, decades pass and one of the few times Soul Train was in reruns, I discovered some new ish (because hip-hop was dying, rock-rap wasn't far behind and neo-soul was starting to sound alike). Anyway, I have a new respect for this man and hope they do an Unsung episode for his musical contributions.