I'm pretty confident Azarenka is going to win pretty comfortably tomorrow. Kvitova has been up and down this tournament while Azarenka other than the obvious Bartoli tank which she still could've won 6-2 6-2 if she gave any effort has been in great shape. She's just as powerful as Kvitova and will force her into error.
Reason?
Offence: Kvitova = Azarenka
Defence: Azarenka >>> Kvitova
The only way Kvitova is going to win is either a bad day at the office from Azarenka or hitting 70-80 % first serves in the corners
On Kvitova you're right, she's been very up on down... her match against Wozniacki and the first set against Radwanska when she was down 1-5* were her best display of tennis IMO...
Petra has some very big physical lapses at times where she's slow, sluggish etc... with her footwork and that automatically brings tons of UEs in her game... against Vika's consistency that might not do it.
That said, Vika isn't a pure offensive player... Vika is some sort of consistent power-hitter able to hold good high cadences for a long amount of time... Vika has good defenses and she always makes you play one shot more with her relative medium-fast pace shots... she takes the ball early and this combination of things makes it very complicated for bigger hitting players or more offensive minded players who aren't at the top of their game to play her.
That's certainly what Zvonareva experienced and if Petra comes like Zvonareva, could be fairly in Vika's favor... on the other hand it'll all'bout Petra.
Another proof of this is that Vika doesn't hit tons of winners nor does she strike tons of UEs... she plays an excellent level of controlled agression mix of some winners here and there, low or relatively low UE count with a good amount of FEs and it's the winners and high FE count that makes her game good. At the difference now, 70 to 80% of Petra's game are composed of risks, high winner and UE count, the rest FEs are barely something she relies on though it can be high because of her power, surgical placement and weight of shots.