You aren't clear on your criteria for luxury (service availability and training, decor, technology standards, etc) so I don't know what you are looking for, but I definitely think that there are some very nice hotels in Havana. Granted, I was there on a US gov't approved visit and only was able to stay in our approved housing and a B&B but I had drinks at some of the nice hotels in town and thought they were great. I would love to go back and would probably split my time in one of the nice hotels (ie Hotel Nacional which has a great lawn overlooking the Malecon and bay) and a B&B. The latter was great since you had a chance to speak to locals- the owners of the B&B, the neighborhood folks, etc- about life which was so intriguing and special.

So, for luxury hotels consider checking out Tripadvisor reviews to pick a spot. Staying in old Havana is nice because of the location but Hotel Nacional isn't too far from things. Depending on your luxury standards also consider a home stay/B&B. It's great!

Enjoy your trip. Cuba is stunning, intriguing, and beautiful. You're lucky to be able to travel there!