My wife and I recently spent 2 weeks in Buenos Aires and had stays at both Sheratons and the Marriott as well. No real complaints about any of the properties except that at the Liberator the housekeeping staff (or at least I think it was them) were opening and closing doors quite frequently letting them slam shut everytime starting about 10am and lasting until 2pm or so. So if you are a late sleeper this could be a potential problem there.

Other than that I didn't have any complaints with my stay there but I wasn't overly impressed with the hotel so I would rate my stay as just "ok".