I had Izotope's Vocalsynth (1, yes there is a 2 now) and when I discovered Manipulator I liked it a lot better. It works really well from the extremely subtle to the extreme, and features such as the smooth grains when pitch shifting down are effective. I can't say it's "better" than any other similar tool, only that the UI, workflow (easy to do the MIDI routing) and sonic quality is superb from my POV.
I was fortunate enough to capture this on a really deep sale. I don't remember how much it cost, but it was far less than $149.