I, personally, like to toss scoundrel, geomancer, and hydromancer on every one of my characters.
Scoundrel for "the pawn" talent. I cannot overstate how useful minor re-positioning is, especially when it's free.
Geomancer for the physical armor healing. Fortified counters decay, and thus is incredibly useful for healing.
Hydromancer for HP and magic armor healing. Magic shield counters a lot of magical CC, as well.
For bonus points: If your build doesn't provide access to a mobility skill (for example, you're not running huntsman or warfare or anything else with a jump like "tactical retreat" or "phoenix dive") then you can spend only one additional point in scoundrel in order to gain access to "cloak and dagger" on that character.
For melee characters, I recommend each one take one point in polymorph. That point provides a point of strength to go with it, and you gain access to the bull horns skill, which provides a method of damaging people with high armor in order to help your magic damage dealers out and exploit low magic defenses.
For caster characters, I recommend investing a couple points in necromancy. Necromancy has a few skills that deal damage to physical armor and scale off intelligence, again providing a way to deal with high magic armor characters.
This is definitely my personal style, but I'm a huge fan of "toolbox" kits. If anyone at any given time has at the very least the ability to heal and deal with any type of armor, you can easily and effeciently answer most situations that arise.
