For me, the answer is backing and then melody, because that's the order that I think of it in.

It's super-easy to create a simple backing track in BiaB to import into SynthV.

So even if you know the melody, I think it's always better to hear the melody against a backing track, because it helps you make all sorts of decisions.

You can play the melody track into SynthV via a MIDI keyboard in the stand-alone version. You can slow down the tempo if you're not a good keyboard player, but the backing track won't follow when you do that. But you can still mute the backing track play to the click of the metronome if you need to do that.

Or - if you're really lazy - play the rhythm only, and drag the notes to where they need to be.

-- David Cuny
My virtual singer development blog

Vocal control, you say. Never heard of it. Is that some kind of ProTools thing?