I think as a concept show Butterfly would work best. It's Mariah through and through. But in terms of what would work best as a show, I think Daydream makes sense. Butterfly vocally has too many songs that I don't think would translate well live, like 'The Roof', 'Breakdown', 'Fourth of July' and 'Babydoll'. Whilst I love those songs, they're too intricate with layering and soft vocals that it wouldn't quite work live. Daydream has a more straightforward lead vocal throughout. Of course, both would be very difficult for her to do live now
The beauty of a show like this would be Mariah re-arranging the intricate songs, stripping them down to a few essential elements. Think about how well "Breakdown" worked acapella on the Rainbow Tour
just as a snippet. It's because she showcased the melody and sang in a comfortable range.
Obviously she can't be making every song into a slow number otherwise it'd be sleep sleep and "Honey" only can't carry the show as a uptempo, but live arrangements doesn't necessarily mean acoustic ballad.
In that sense TEOM would translate well as a live show, because the majority of the songs don't need big work. They're already raw and ready to be done live, they were born like that. We also saw a glimpse of what the Emotions album would sound like in this context with Unplugged, which had 4 of its 10 songs. An album like Butterfly would make for an interesting show artistically, to display Mariah's musical genius. Daydream or the debut too, I think.
An interesting concept for a one off in Vegas perhaps or even an overseas treat.