I have Melodyne Assistant on one machine and Editor on another. Assistant was a night and day improvement over V-Vocal for ease of use, lack of artifacts, tools, improved sound, auto-handling of formants, etc. It is much easier to visualize what you are doing and make delicate edits. The free video tutorials are fantastic.
One thing: in the top right corner of Melodyne you can right click a square and choose the time grid display and the snap properties. I highly recommend NO SNAP, and that is not obvious if you don't know. With NO SNAP, double-clicking a blob/note with the pitch tool will still snap it to the right spot, but you have the option to slide the blob freely. Sometimes you want to slide the note to a different pitch and then double-click, or you may want to slide the note slightly off-center of the pitch because of the way the pitch slopes (rises or falls). You will see what I mean when you get there, but this is a feature that is not necessarily going to jump out at you.
I have had some Melodyne crashes, but I had a ton of V-Vocal crashes.
EDIT UPDATE: I have Editor on a second machine and I don't want to give an opinion too quickly since I am very experienced on Assistant but still new with the polyphonic version; however, the polyphonic version was not the miracle I hoped. When I used it with an electric guitar part, I got so many false positives and random blobs, that it was a complete mess. I am still not sure how it would work with a choir where one person sings the same part several times. So, bottom line is, I would be happy forever with Assistant, but I may love Editor later.