I often write portions of songs... verse, chorus, etc,  then try variations of the vocal notes using midi and playing around with the notes in piano roll.  Also helps in working out harmonies.
Does anyone else here write out vocal midi tracks before recording the vocals?  and my question is:  what synth/patch do you use to emulate the voice when listening to the mix to decide what is best?  I've gone thru many patches in different synths and haven't found one I really liked, but was wondering if anyone did this and had a patch they liked to emulate a midi voice?  Does this make sense?  Maybe I should use Melodyne with recorded single-note vocals and test note variations moving blobs around that way?

I tend to use a plain piano patch for working stuff out.

I typically record vocal first then build the harmony around it; but even if simply hummed into a microphone, a mock "vocal track" can pick up variations and inflections not captured by MIDI. This option (plus Melodyne if needed) may be an alternate option for you as well.

I use the bongolese method.

I use clarinet-type of instruments to imitate vocals. I always make a MIDI track of the vocals to get the notation for it in case it would be needed one day.

For me, I usually record the desired melody line using a flute patch - it seems to work best in that a) it stands out in the mix, and v) I can hear it when I sing along with it - it doesn't interfere with the vocal sound layer.
 
a trombone patch also works quite well.

I also tend to use a flute, or sometimes a recorder or clarinet.  It is certainly easy enough to change to something else, if needed.
 
Bob Bone
 

Clarinet for me.
 

I use either guitar or piano (real guitar, not Midi)

It's just a placeholder, but I try to choose a sound that mimics the characteristics of a voice, just so the sound fits together.
 
Bob Bone