I intentionally left out Celestia + Luna, because I know what would have happened if they were an option.

^ Lol yeah

the rarity + sweetie belle duet should have happened in sisterhoof social

Where's "All of the above?" ;)

Seriously, I want to see the development of the relationship between these two sort of "honorary sisters."

ALL OF THE ABOVE. ALDFKJSDLKFJSADLHGJDLSKFJDSFHDSFDF
I would flip out with ecstatic adoration for any of these. I'd love to heard Applejack and Apple bloom sing again; I love AJ's voice! Rarity and Sweetiebelle have beautiful voices; it would be just so sweet and beautiful to have them sing! Rainbow Dash and Scootaloo really need to spend time together; RD should teach flying lessons. And a song would be superultraextremawesomazing.

The idea of Spike singing a song is really growing on me. And I like Twilight and Spike's relationship. Twilight is sort of matronly to him, yet they're good pals. :)

All of them!!!!! WE NEED 'EM ALL!!!!!!!!!!!!

Indeed

This would be adorable!

Hmm true

Both of their voices are amazing!

If it was an option I totally would have picked celestia/luna. But I also really want to see spike/twilight. Possibly singing about how twi is like spike's mother in a way.

Yeah true

Like when Rainbow Dash is trying to teach Scootaloo how to fly or something.

I think Scootaloo only sang once, and that was in Bad Seed