Pallis is superior to Valerie when you need that extra push in dps with her active. Other than that, Valerie should be your go-to unit in these situations. Being a male unit means that he will probably have better base stats (my 50cc50 Valerie has almost 550 ATK with max lvl Prince + Savior title iirc) and he is superior in this map because his skill allows him to clean bigger waves faster (and you also have a Barbie, which is essentially an upgraded Valerie).

Bernice is a really good choice and you won't regret it. You can manage these additional costs by making sure Katie stays alive after the Troll gank squad so she can pop up an extra skill for +15 UP. Remember that Echidna has a bit less range than normal healers. Take that into consideration when planning to deploy her.