I stayed at the Atelier Montparnasse for 4 nights in total, one of those nights was in a Havana Suite. I stayed my first night in the fancy Havana Suite and thoroughly enjoyed the amenities that came with it, a luxurious tub, Nespresso machine, and fantastic view of Montparnasse's streets, classic Parisian. The next day I headed out to Mont St. Michel, and the wonderful staff at Atelier gladly held my giant backpack, so all I had to take was an overnight bag. When I returned I stayed in the one of the standard room, no special amenities but a comfortable bed, wonderful rain shower, and a decent view. I would have loved a Nespresso machine in the second room, and it would have been snug for two people.
My advice: if you are alone, one of the standard suites is fine, but if you are traveling as a couple, upgrade to one of the suites, they are fabulous. I skipped breakfast because there are several boulangeries nearby. Oh, and there is a metro stop a block away.