Without a doubt: Rate of Learning.

I've recently come to this realization after years of work. Rate of Learning dominates everything else. Teammate doesn't have good communication skills? Are they willing and working to learn?

Rate of learning is more important than intelligence, skill, mindset, or demeanor because it's the rate at which those change.

Choose someone who learns exponentially over someone who learns linearly.

Avoid people who aren't interested in learning like the plague your life may very well depend on it.