Looking from what you have it depends on how you want to roll: 2 Gold 1 Silver vs 2 Silver 1 Gold.

For the former, Mehlis and Barbie are the choices no question. I've said before that Cyrus has his place, but here you have mages better than him even before you rolled him so its better to go with Mehlis and Barbie here. For the Silvers, if you do need a third to do a map, it depends. Valerie at 50cc50 at 100% trust caps out around 440 attack power and Pallis at 50cc50 at 100% affection caps out at 446 attack power. If the question is raw damage Pallis is your girl for the Silver mages since her skill is also an attack steroid, so that adds to it. For Valerie, that depends if the increase in splash radius actually leads to a damage increase for big clumps of enemy units, given from what I'm aware of how mage attacks work. So depending on the situation its a toss between steroid or bigger splash damage.

For the latter, we only have 2 Silvers as of now so its no question. For the Gold mage position, its another toss up. Barbie has Val's splash increase but bigger. And I do mean bigger (2.0 vs 1.5, yes the .5 difference is definitely noticeable). Mehlis on the other hand has higher attack (505 attack at 50cc60, 100% affection) than Barbie (475 attack at 50cc60, 100% trust) and comes with a range steroid so she can be hitting things much sooner and for longer since her attack radius is larger during skill uptime.