I used to use a Digitech Vocalist II. It was passable. Have they improved? What are you all using?
For live performances or for recording?
For recording it's pretty hard to beat melodyne... it provides so much control
For live performance, depends on whether your primary focus is on pitch correction or harmonies. THe Voiceworks is better at pitch correction, but based on what I've heard from you, pitch correction is probably not an issue.
I have both Digitech Vocalist and TC Helicon Voiceworks. I think both units are pretty good at harmonies. If you plan to use MIDI to change patches and set parameters, I think the Digitech MIDI implementation is somewhat easier than the TC Helicon.
For example, if you create an instrument definition file so you can enter parameters from the menu, the Digitech lets you create the menu in a way that lets you pick KEY directly from the menu as a letter, whereas the TC Helicon makes you enter the key into the piano roll as an integer, which I find to be somewhat less intuitive (0=C, 1=C# etc)
Forgot. Live harmonies. The Digitech Vocalist II that I had was easy to use and effective. I was sort of wondering if anyone had used or heard that unit and if the newer ones are better sounding. If the new ones are about the same quality sound wise I may look for a used Vocalist II on EBay