This really depends on what you're looking for. Each option has inherent advantages and disadvantages.
Antarctic expedition ships like Nat Geo Explorer can offer more active itineraries, taking you well beyond the tip of the proverbial iceberg. These ships carry special gear and equipment and their teams include specialist outdoor activity guides.
If you are active and love to explore, an expedition ship is probably the best option.
Luxury ships tend to be larger vessels, with a focus on physical comfort, fine dining, and on-board entertainment. The amenities and accomodations offered on these ships are leagues above many of their expedition counterparts. From cabin quality to onboard activity options, luxury cruise ships are a superior option for those prioritizing comfort.
That said, many of the luxury cruise ships serving Antarctica have capacity for 200 passengers. The largest of these ships support over 400. In many cases, this increased capacity comes at a disadvantage to active adventure seekers.
To start, IAATO guidelines prohibit landings by ships with more than 500 passengers. It's also important to note that no more than 100 visitors may land at a site at any one time. If a ship carrying 200-300 passengers makes a landing, it often has to be split between two nearby locations or consecutive landings. This means less time at the landing site for passengers or fewer landing sites during a cruise itinerary.
We wrote a detailed guide on most of the available options serving Antarctica that you might find useful:
Please don't hesitate to reach out if you end up with any other questions beyond what's covered in the guide.