I typically go /sch if I'm going to use a mage sub. I only rarely pulled out the /whm for teleport spells doing a quest recently.

/whm you will get cure4 and reraise, plus status removal spells

/rdm you have enspells and phalanx.. and your magic skill will suck.
I would only really use it for magical WS... ie brewing on bst.
It has many other useful spells as well, but mostly you'll have better or more powerful options w/ /sch or /whm