Note: This is speaking strictly about C6.5's VariAudio (VA) - I'm on C8 now for my own stuff but the place I work out of now runs C6.5; I have a feeling C8's will be much improved but I haven't tested that yet.
It's the only tuner I use while tracking, but it only makes a final product like 10% of the time. It's great for getting a crappy singer roughly in tune to track harmonies or doubles, for writing harmony lines off of copy/pasted original parts for the guy to use as a reference to sing to, but I always abandon the changes and tune with Autotune Evo (AT) for the final thing.
I've found that if I A/B a track done with VA and AT, the VA track might sound a touch more realistic, but it also sounds more out of tune for sure. You'd have to do VA 2-3 times to match the accuracy of AT, and then it's just going to sound super fake.
The other real issue with VA is that the segment detection is really bad and you have to chop rises/falls in pitch off of every note for it to sound realistic. That, and you'll probably already have noticed that it's not great at always giving you two distinct notes when the singer obviously changed pitch, and you have to manually chop the tuning region into separate parts (hit tab to quickly switch between tune/segment modes) which really sucks compared to AT.
FWIW I also prefer AT to Melodyne, but more for workflow in Cubase than fidelity or timbre or accuracy. I still use Melodyne's standalone program to tune bass DIs, however (VA has no chance at that, can't detect low pitches very well).
Again - I'm guessing it's better in C8, but I can't say for certain.