To echo what others have said… VA for quick fixes, integration is great and it’s MUCH improved since its initial conception.
Then it should be as easy to use just as VA already is:
Once upon a day I hope we’ll get ARA implementation in Cubase. If something weird is in my mind, I definately use Melodyne - this software has gone a long way from simple vocal correction to… magic mushrooms for your ears Absolutely unrivaled in this regard! If the job is to tweak a good vocal performance closer to perfection I usually use VariAudio just because it is simpler and sounds great. basically the same story) to get transparent results. Anyway, MDs analysis may also need some manual rework (again: cutting segments, so called ‘blobs’ at sibilants, slides etc. It allows a unique approach of how the sound can be influenced.
Melodyne 4 is king when you have more problematic or polyphonic material or want to go wild on sounddesign. As Manike mentioned you can get great results when you use it as a tool, not as a robot, reworking the segmenting when needed (cutting sibilants and slides) is essential.