I used Avanna for this. I have Sonika, but don't find the quality as good, even though I do like the style of her singing.
The use of a vocaloid in this one was a temporary thing - it helped me explain a few problems to the lyricist and will also help me avoid the issues of having to explain to the singer what I'm looking for rhythmically. I'm in the process of getting a singer to do the final thing. It turns out the girl who recommended Adena (who sung Carefree Days) is a great singer herself. Just modest, and in her defense, not looking for solo vocal work - she's really a piano player. I may well go back to Adena (Cahill), but would like to try others on other songs first. This is new territory for me, and so don't want to limit myself at this point by working with just one or two people. Tiffany (who I want to use on this song) is one of my favourite people in the world. I know she will put 150% into it, at least.
I will first be recording a male vocal this weekend on another song (Tiffany's boyfriend as it happens!)... I'm not so happy with the shape that one is in at the moment, but want at least a scratch vocal down before I make any more changes - you can hear that one here - http://www.studiobeemusic.com/vocaloid/nomansland.mp3.
This also originated in BIAB, though has transformed in Cubase more than any other I've done using BIAB so far. I also used vocaloid Avanna on this sample, dropping down an octave or two to get into the male register.
What Vocaloid did you use?
Why didn't you ask the singer of "Carefree".
She's got a wonderful voice and you haven't revealed
her name yet.