I selected Quark and the Ultramarine for a group trip to Antarctica based on their strong polar operations history, the comfort and amenities of the new ship, the excursion opportunities, and the expedition's itinerary.
And, while I don't have personal experience traveling to Antarctica with another company to compare against - I felt that Quark delivered on all of these key areas.
Here's what really stood out to me:
New ship. Cabin was well appointed and spacious for two. Balcony views were amazing.