you don't need a secondary school, period. doesn't matter what school you are~ they are useless.
that said, if you are concerned about death's lack of an attack-all spell and are below level 48, go with myth as your second. you will have 2 attack-all spells to use, and your spirit blades will be good for both.
I find with any school it's best to try to be very careful with out of school spells. Wait to get them till you are really sure you need them. Training points can go fast and the quests to get them get harder as you advance in the game.