But based on this list-Easily Rihanna.
That was her best Era quality wise. She had a great image and everything was amazing. I STANNED for her hard during that Era.
It was between that and Born This Way, but the music on Born This Way itself isn't really that dark, it was the image with the black clothes and the horns.
While the music on Rated R is about pain, murder and heartbreak, and Rihanna herself had also a dark image at the time.