Capable of holding one's own in a conversation, and to make me think (come on, when we're debating religion, don't use the Bible. I can use it too and I'll win)
Capable of admitting fault
Patience (I know I can be tiring)
S-types (particularly SJs, sorry Guardians)
Conviction that one is always right and I'm wrong
Of course, there are more in both lists, but there you have it. Sorted in no particular order of importance.