I've used melodyne editor for quite a while. It's really good and transparent on moving pitch a step or less. Beyond two steps, you have to go to the formant tool in many cases.

It is also dependant on the pitch of the voice and whether that voice is upfront as a soloest or a background singer.

Personally, I haven't used the format tool much since I generally get really close to the note. However, on the few occasions I experimented using melodyne to create harmony tracks, using the format tool and attempting to get the vocals to sound natural was an exercise in frustration.

I'm not saying it can't be done or you can't change the vocal timbre so it sounds good or like someone else is singing, but it's going to take time to get it right and once again, the less you move the note from it's original pitch, the easier it's going to be to get it sounding right.

That's been my experience.

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