It's so tough to predict where they are going to sign, and that has an impact both on the expected salary, as well as the volume, as well as the production.
Ideally for you for Mrzaek, he re-signs in Carolina on a contract similar to Grubauer's or Hutton's (big enough to be the starter, but not enough to hurt you badly in a cap league).
Ideally for Varlamov, he gets a fresh start away from the new Grubauer contract. Where would that be? Replacing Bobrovsky in Columbus, Replacing Smith in Calgary, or maybe even taking over Mrazek's net in Carolina (backed up by McElhinney or Nedeljkovic. He probably commands a little more than Mrazek, maybe something similar to what Koskinen got.
That being said, the goalie market is fairly saturated right now, and with Lehner, Bob, Smith, Elliott, Talbot, Kinkaid, etc, all hitting free-agency as well, there may not be enough spots to fill. Especially if we see a 1A/1B situation get traded away. Perhaps one of Halak, Khudobin, etc are seen as a stopgap starter to a young stud. Really tough betting a lot on a FA goalie right now. You could have a Lehner on you hands for next year, or you could have a Grubauer.
If you're looking for the one of the two most likely to get a solid starting job for next year, seeing more starts, regardless of contract cost, my bet would be Varlamov.
If you're looking for more contractual value, with some likely solid ratios, I would pick Mrazek.