Are you doing full score choral with all parts? Or is this for a single singer and you don't know if they're singing the top or the bottom?
If it's full score, I'd break them out into two separate lines.
If it's a line-by-line for a single part and you don't know which to do or you're specifically asked to do both, I would use in-accords to show the separate parts. If the singer is asked to sing the bottom line, it's a 100 times easier to skip over an in-accord part and read the notes she's supposed to sing rather than figure out intervals for each note.