Are there any books of the Bible that you have purposefully avoided in preaching?
If "purposefully avoided" means that I think I should preach them and I won't preach them, then the answer is no. If "purposefully avoided" means that I chose one over the other, then yes, because I can't do Romans and Isaiah or Romans and Deuteronomy.
And I base those decisions on the perception that, given where the church is, who I am, and what the nature of the culture is, it seems at this point—all things considered—most profitable for the church to do this and not that.
But there is no book that I know of that I have said "no" to because I don't want the challenge or I think it would be bad for the people.
I know some would be harder than others. Revelation is the one book that John Calvin didn't write a commentary about. I wonder why? And I would find it hard going to know what to do with the middle chapters in there. Same thing with the last chapters of Daniel. Same thing with Ecclesiastes. Those would all be difficult, but I don't think I've avoided them because of that.
In fact, I've sometimes wanted to do them just for the challenge. And yet, those books in particular have never seemed as edifying as the ones that I have chosen at the time.