Which pitch correction tool you use depends to some extent on how you want to apply it.

With plugins like Melodyne, there's a preprocessing step which identifies which chunks of the audio are at what pitch. You can then move these chunks to the correct pitch.

With plugins like Auto-Tune and GSnap, analysis is done on the fly. It's essentially instantaneous - it only takes a single wave cycle for autocorrelation to latch on to the frequency.

But once the pitch is identified, the plugin has the task of "pulling" the wave to the proper pitch. Unless you're going for the Cher/T-Pain effect, it'll take a moment or two to pull the pitch to the correct frequency. This works well if the pitch is fairly close to the target. If not, there's a bit of a "scoop" as the wave is brought up to pitch.

So if the correction involves changing the pitch, something like Melodyne (which allows chunks to be shifted) is probably the best approach. It also lets you adjust the forment, so the timbre of the shifted pitch isn't out of character.

If you're more concerned with staying on pitch, something like GSnap is great in keeping your held notes from going flat.

Of course, it's always best to re-record the note.

If you're on a budget, you can also manually pitch-shift the offending bits to the right notes, and use GSnap to stay on pitch.

-- David Cuny
My virtual singer development blog

Vocal control, you say. Never heard of it. Is that some kind of ProTools thing?