Similar to Roberts81 warning on Westwater, I would stay away from Browns Canyon if you classify yourself as beginner/intermediate. At these flows it is a bit more forgiving, but still several moves to make in Pinball and Widowmaker that could pin your boat if you don't take the right lines. Browns is an intermediate level run. At this level, Upper C has a couple rapids, but more forgiving than Browns. Ruby Horsethief has no signficiant rapids at all.
Upper C and Ruby HT are you best options and I would do Ruby HT if you are going without other boats. Both have details on respective websites (might both be BLM, cannot recall) that tell you what you need to have and give you a sense of the water. Also agree that you should pick up Colorado Rivers & Creeks. I wasn't aware that was hard to find now, but it has tons of good info.