In general, if you've known me for any length of time, you will typically address me as Chris. No big deal. It's my name. I answer to it and everything.
But my name is also Christopher. It is my full (first) given name. I answer to it as well. And in professional scenarios, initial meetings and other more formal situations, I will often use Christopher over Chris, at least until I develop more formality with whomever I'm dealing with. It also doesn't hurt that at my current job there is already a female Chris that I work with, so calling me Christopher alleviates some ambiguity.
I kind of like the sound of Christopher these days. I'm not sure where I made the switch of preference in my mind. I don't particularly want to make people address me in one way or the other, and I think because I'm called Christopher less often, it just sounds a bit novel these days.