All three are starters for their teams. Varly has Pickard nipping at his heels but I think he will step it up and keep the starter crease for most of the final stretch. Halak is down for at least a few weeks so Greiss is in and Dub is playing well in-front of a good squad. I would also say they probably all have about the same odds of winning any game they play in.
In order of most to least riskiest I would say;
Varly
Dub
Greiss
Ideally you want to take a look at what the rest of the season looks like. How many games does each team have lest to play? How many of those are on a back-to-back? That should give you an idea of how many starts you can expect from each. You could take it one step further and evaluate the caliber of the match-ups too. If one has a much easier looking schedule they may be the better option. So no real answer but some structure to follow for some research.