Lounge and Spa rooms are a more modern design. Palais Imperial rooms are more traditional. Moving from one side to the other is seamless, more marble in the Palais Imperial, more avant garde on the Lounge and Spa side. The Suites offer the best views including the Medina walls off to the left.
As I understand it Lounge and Spa consists only of Luxury rooms and Junior suites. Palais Imperial offers Luxury rooms, Junior suites, Prestige Suites and Opera Suites.
Luxury rooms in Lounge and Spa are probably better than Luxury rooms in the Palais Imperial.
Depending on what room type you book and possible upgrades Palais Imperial offers more upgrade options. I would probably book a junior suite in Palais Imperial again with hope for Prestige suite upgrade. If booking a Luxury room I'd probably be more inclined to the Lounge and Spa. The difference is marginal as all non room facilities are common to both.
When I booked Palais Imperial was taking part in a Super Sale with complimentary breakfast whilst the Lounge and Spa wasn't, that finally made the decision for me.
I don't know if they would swap you between the two sides of the hotel if upgrades worked out that way.
Last edited by cwl; Jan 11, 2018 at 2:20 am
Reason: Additions