During our visit to Havana, Cuba, we opted to stay at a casa particular. The local people have since shortly been allowed to rent rooms for turists. Our host Julio was a pediatrician-turned-to-casa-renting. His wife Elsa and her old parents were helping out and the atmosphere in this casa was very cosy and homey. Not to mention that it was very cheap: only about 30 dollars a night.
One night we forgot our key in the room and had to ring the doorbell to get in. No worries, Elsa's dad dropped the key - attached to a string - to us from the balcony. I think casa particular is definately the way to do it. Although we, too, went to a luxury hotel for our last night -- since it was the New Year's Eve and all.