I have melodyne and Nectar (oh and a very very old version of Autotune somewhere or another!)
My preferred way of working is:-
1) Get the singer to redo it properly if at all possible
2) If not Melodyne for minor pitch correction
3) To be honest I got Nectar on a very special offer (with Alloy I think?) and have only used it occasionally and I don't think ever for pitch correction
Nigel