Medium, always.
It's fine if it's a little over or under that, but not too far over or under.

I have not been convinced that a particularly rare steak tastes good and the flavors in looking for haven't developed yet since it isn't cooked enough, but once you're past medium well, you might as well not be eating steak; it's dry, the texture is all wrong, and the flavor has changed once more.

a good medium steak with some mushrooms is divine