Vocodex is the best on the market. Own (or have used extensively) every single one available including those from Softube (UA), iZotope, Melda, Zynaptiq, Native Instruments, Sonivox, TAL, etc.
However, Vocodex is a pretty deep plugin. You have to read the manual or watch tutorials. It has A LOT of features (not all of them are intuitive) and is capable of a huge range of tones / styles. Most people likely don't even get 10% into what it actually does.
Here's 10 Part tutorial series:
(Unfortunately can't link playlists here, so I think it's linking to 1st video in series).
Agree with others - waiting to see what happens with Orange Vocoder - it used to be my favorite for software (nothing beats hardware yet). But Vocodex completely blows it out of the water, so they got to up their game on any future update.
This video does a somewhat decent job of going through some of the range of styles Vocodex does - but it can get WAY crazier than this, as this video doesn't even touch on the band editor or midi triggering, which is 50% of the fun: