Title kinda says it all.
I would prefer a single class change over a race change. Loads of folks have been wanting class changes for a while, myself included, as I do have a toon with every class, but I spend 80%+ of my time on one specific character, who I have been wanting to play as other classes for some time. It is a much simpler change in my opinion, (excluding thoughts of mechanics or stats, skills, etc), just simply because, speaking for myself personally, I am more attached to my character than their class. All my characters names are lore friendly, so a simple race change is not going to sit well with me, or many many more people because than we would either have to live unsatisfied with a incorrect and immersion breaking name, or fork over the money for a name change. For a lot of people who have been sticking to one main toon for a long time, they are attached to that character, and people also know/recognize them for that very same character.
If this is going to happen, ZOS should be at the very least be giving over a race and name change, not just the former.
"You are brave and you are strong, of this there is no doubt. But without me at your side, your deeds will go unknown, your death unwept and your story unsung - Sings-In-Shade, the Argonian Bard