The Bar/Lounge at Hotel Plaza
The bar/lounge at Hotel Plaza is acknowledged by those who travel for a living. Of the 3 professionals tracked on TripExpert, 2 mentioned the bar/lounge, such as Frommer's and Fodor's.
Hotel Plaza 
Frommer's
Fodor's
Frommer's "And, by all means, come by for an afternoon drink at the rooftop Solarium Bar, with great views of Havana and the neighboring Bacardí building"
Fodor's "It boasts no less than three restaurants and three bars, so you're never too far away from a decent meal or a mojito"
