To be honest, I went back and forth several times on which one I thought would be easier. It's extremely dependent on the skills and personality of the person in question.

I ended up deciding the people skills would be easier to teach because, frankly, the culture of the field demands a lot more in terms of technical skills than it does in people skills. The bar is set a lot lower for people skills among developers than it is for programming skills, and in my opinion, pulling someone from "horrible" to "competent" communication is easier than pulling someone from "ok" to "awesome" as a developer. But the truly skilled, in either area, are hard to find and worth their weight in gold.