Fire and Lightning are still pretty good, but one of the reasons Cold is a bit better, esp for HC, is that it applies Chill and Freeze, which is another form of mitigation.
Witch is still very good for a MM build. Just be aware that a minion build takes a while to get going, as zombies and skeletons are fairly weak early on. You'll want to mix in another spell while going through normal, and you'll need to be aware that bosses tear through your minions pretty quickly (though you can spam skeletons on top of the boss to keep them occupied). Also, getting a Rejuv Totem early-mid on can help keep your minions up a bit longer.