As someone who also booked for the first time recently, reading through the last 15 pages were incredibly informative with lots of pics thanks to FT contributors. Should make it quite clear that the safe choice for a first time visit is easily Suk57 or Marquis.

However, which one you choose ultimately comes down to preference. Marquis is slightly more expensive and still has some parts under construction for another couple of months. And yes, you will get complimentary lounge access and breakfast at the Marriotts. As I recall, plats should get should get suite upgrades at both.