We used the third vendor - Regal China Cruises - on the Empress Sheena nearly four years ago. I have heard from others (but don't know from personal experience) Viking and Victoria are as good if not better. We chose the Regal China as we had very little flexibility around our departure date. They were the only one of the three with a sailing date that worked.
We went for the scenery, not for the boat. Cabins were about 140 sq feet with two lower bunks (couldn't push them together). The passenger mix was 1/2 Chinese citizens and 1/2 Western (mostly expats on holiday). The scenery was spectacular and we learned a lot from taking that trip. Glad we did it, have no inclination to repeat it.
Breakfast was by far the best meal. All food was buffet style, with both Western and Chinese cuisine. It was average with a few dishes simply awful. Nothing was a standout on the buffet. We enjoyed our table mates - a couple from the UK and a couple from San Francisco whose parents had emigrated to the US many years ago.
We took the sailing from Chongqing to Wuhan. That went through what's still visible of the Three Gorges and through the new dam. Side trips were included - we got off the ship for an hour or two once or twice a day. We didn't have the flexibility of simply stretching our legs. We either went on the tour or stayed on the boat.
This was a three or four night sailing. It was long enough to enjoy the scenery and short enough to make the overall experience good. A seven day sailing sounds too long to me - better to use the days to fly to Guilan and enjoy the Li River area and/or Chengdu (once it's had time to recover from the earthquake) to see the pandas and enjoy the considerable variety of things to see in those areas.
Cheers, Anne