A bit late to answer Pattonxls question but maybe others will be looking for an answer to the question.
There is no real issue with the type of bag required for a polar cruise. Suitcases are fine as there is storage available in cabins. Having said that you should avoid bring very large suitcases.
Note: If you are sharing a triple or quad cabin on a cruise I would double check with your operator about the cabin size. In this situation I would bring a backpack or duffel as they are easier to store in confined spaces.
Baggage weight limitations will usually determine the size of your bags anyway. It is important to make a note of the baggage allowance if you are taking a domestic flight from Buenos Aires down to Ushuaia as the allowance is less than International flights.
When you arrive at the ship the crew will usually assist you with luggage and you can unpack your items and stow the case/backpack/duffel etc. until the end of your cruise.
If you are staying at a hotel in Buenos Aires on the way to and from Ushuaia then you can request to leave excess luggage (such as warm weather clothing for Buenos Aires) at the hotel for your return. This enable you to reduce your baggage weight. Just pack a smaller lightweight sack or bag that you can leave at the hotel storage facility.
Remember that there may be laundry facilities on board your ship as well as facilities in your cabin to wash clothing. You can pack a small bottle of biodegradable clothes wash at an outdoor store. Wash your synthetic fabric clothing in your cabin. These items dry very quickly.
Be realistic with your packing. Layout what you think you'll need, identify the necessary items and you can probably then halve the amount of everything else! Also don't leave your packing until the last minute. Give yourself plenty of time to go through what you need and try to dump the unnecessary items.
There is plenty of good information on this site about clothing to bring etc.
If you have any other questions I'd be happy to answer,