The more resources, the better.
I'll take a look at their choices when I have spare time, will learn something new
Problem with Witch (and Kraken) is they don't benefit much from any set.
Bolt is at least somewhat decent for Witch, so she can land her blue stun faster.
But I did forget to mention attack speed anywhere for her, will make sure to add it in the next update.
Armor is helpful for her, so is magic resist and health. I just prefer to use tree for damagers, since it's universal, but it probably isn't best for everyone. So if you have bad tree runes for a damage hero, but have decent rock (especially for front- and back-liners) or mist (especially for front- and mid-liners) ones, use them with no regret.