I've been once, just this past December. The scenery is amazing, especially the west side of the peninsula; Lemaire Channel, The Gullet, Paradise Bay, Neko Harbour, Wilhelmina Bay are all wonderful as are many other locations. There are plenty of penguin colonies, seals, whales and various birds. I would decide if you want wildlife, scenery or a mixture of both. I have not been to South Georgia Island, but as
@thedigitalbean said, it is probably the best for pure wildlife. I echo there are many options. If you want other mammals, you have to go north, not south. The scenery is endless rock, snow, ice and glaciers.
It is an experience of a lifetime; I highly recommend it. I did a Lindblad Expedition, which was NOT a dedicated photo trip, and it was 125 passengers. As Graham and others have pointed out, I wouldn't go with a larger group than that, and if you wanted a photo dedicated trip I would target even smaller groups. The newer ships are real wonders of engineering. I could even use a
tripod from the ship.
I think the actual South Pole and much of the mainland of Antarctica is not as "target rich" as the peninsula, which has many islands and is quite mountainous.
Dave