|Arbane the Terrible|
I had a lot of fun playing a witch, even when the campaign ended up fighting a lot of undead. At that point, you need to use your hexes to aid your allies (War, Healing, Fortune/Misfortune, Retribution at higher levels), and mostly use spells on the undead.
Unfortunately, a lot of your spells are ALSO worthless against undead. :( But mostly isn't all, and witches are prepared casters, so your spell selection is a good night's sleep away from making the undead wish they were REALLY dead. Bestow Curse and direct damage still work, Chill Touch makes undead flee, and Summon Monsters don't care what you summon them to kill.
Armor doesn't affect Hexes - they're (su) abilities, which don't need gestures or words to use (I believe the devs have ruled that you DO need to be able to speak to use Cackle, though). As (su) abilities, Hexes ignore spell resistance.