Been there many times.

Depeneds what you are looking for.

The Novotel is probably one of the newest and most comfortable. Location is not great.

The Nacional is awesome, but very very tired. It is a cool property and has a lot of history and is in a great location, but the rooms are not all that comfortable.

The Havana Libre is a good choice. It is where all of the media stay. Just like a Hilton.

The Melia Cohiba and Melia Habana are also good choices.