We cruised on the Australis as part of a 3 week trip to Patagonia. We did not select the ship; our travel agency did. We were very pleased. The size of the ship (100 cabins) was excellent. The staff was knowledgeable, friendly, helpful and seemed to enjoy what they were doing. Food was very good; having the alcohol included was great. All the excursions were well organized. We received information prior to each one about what we'd see/do and what to look for. On several of the excursions, we could choose the level of activity. The staff also was very attentive to safety. All excursions were made via 'zodiac' inflatables. We were given detailed instructions for getting into and out of the zodiacs. While somewhat pricey, we would highly recommend the Australis. The only negative aspect was on the day we boarded, our luggage had to be at their office by 10 AM but we could not board until after 5 PM. Be sure to plan some activity for the 10-5 otherwise it's an empty day and there is not alot to see/do in Ushuaia.
All cabins were 'outside' ones with a large window. There was sufficient space to unpack and store suitcases and clothes. The bathroom was fine.
Ushuaia is one of the major jumping off points for cruises to Antarctica. Overall the town does not have alot to offer. You can visit the Tierra del Fuego National Park and there is an interesting penal museum (former prison). But overall 1 day in Ushuaia is probably more than sufficient.