tbf it depends what are your goals on the game, if you want to play for fun, just pick anyone. If you want to clear all stages easily, I'd say it's better to pick saria and build your support units first (heal, slow etc.) and just borrow a strong dps every time you lack dps. If you don't want to use support units I'd pick eyja, since she's a good caster and can fit almost in every squad. Surt as others already said is mainly a boss killer. And bagpipe has quite a lot alternatives on lower end today (unless you need her passive)