Oceania supplies a great sounding sample set in a straight forward interface. Rather than trying to be a complete choral phrase builder, Performace Samples has focused and excelled at creating a powerful choral library that allows pros to work quickly and offers just enough flexibility to craft your chosen syllable intent.
Thoughts, demos and more: http://bit.ly/2rgHgiY
 
https://www.youtube.com/watch?v=ED-IKFy-O-Y