(I suspect this query may be more appropriate to the Marriott or Starwood forums, but I'll leave that to the mods to decide. Since this is the Luxury Forum, I'll speak mostly to the luxury brands...and perhaps suggest that this thread change title to "Ranking the Marriott Luxury Brands" to be more appropriate in this location.)

Marriott's luxury brands (based on price qualification) include:

Ritz Carlton Reserve
St. Regis
Ritz Carlton
Luxury Collection
Bulgari
Edition
W
JW Marriott

I've listed the brands above roughly in descending order of my estimation of luxury quality. As with all things, YMMV and I'm sure others may see those in a different order. Obviously, there are stronger properties in some brands that match those in a "better" brand, just as there also are weaker properties that sometimes seem more appropriate in a "lesser" brand.

Your need to have a "best" luxury brand is not necessary. Marriott now has several luxury brands that offer distinct pros and cons. Now you have the ability to choose the experience that best suits your wants from a larger portfolio. Nothing else has really changed thus far.

Ritz Carlton Reserve: this is Marriott's attempt to create Aman-like properties and re-up the RC brand. These properties operate outside the not yet merged Ritz Carlton Rewards/Marriott Rewards/Starwood Preferred Guest loyalty programs. They are usually all-suite type properties in amazing resort locations. They are all new and have a very high service standard.

St. Regis and Ritz Carlton: these are 2 roughly equivalent luxury brands that used to compete but now exist together in the same portfolio. Neither is as luxurious across the board as RC Reserve. There are 44 St. Regis properties and 90+ Ritz Carlton properties. St. Regis only expanded to its 2nd property in 1999, so it's among the youngest of the luxury brands.

I give the edge to St. Regis over Ritz Carlton in terms of luxury and service, but again YMMV.

St. Regis is most known for its butler service, best executed for suite level accommodations, providing central points of contact and service for all service needs of guests. I also think St. Regis is known for its use of technology in rooms/suites. I'd say St. Regis feels like a synthesis of Four Seasons with Peninsula technology. Most StR properties are new, but there are a few older reflags/conversions that require renovation/refurbishment. St. Regis tends towards a modern clean design style of luxury, though there are resort locations that tend to mimic the local architectural and design styles of their locales.

Ritz Carlton is most known for its Club level, offering a higher service level experience than regular rooms/suites with a very nice "VIP club" lounge offering food/beverage and other service assistance. RC properties tend to be a bit larger than most StR, and there are many that are older that require renovation/refurbishment. Ritz Carlton tends to a modern but still traditional design style of luxury, though newer properties tend to a bit more Deco/modern styles depending on location.

Luxury Collection is an assortment of individually managed unique properties, often with historic or authentic, unusual buildings that were converted into hotels/resorts. The designs of these tend to reflect the local styles and traditional culture. These are more unique experiences, with service and style completely dependent on the property and its management team. Some have very high service standards and luxury accommodations that rival the best of the StR and RC brands; others, especially in the US, may be a little closer to luxury-lite, especially with regard to service. There are 100 LC properties around the world.

Bulgari hotels are owned and designed by the famous design house but managed by Marriott's luxury division. There are only a handful of hotels and resorts--and these operate outside the Marriott loyalty schemes, too, being only "partner hotels." Many would consider these hotels to be a lot of pomp with less circumstance, as the hotels are beautiful but may be lacking in luxury service.

Edition hotels were Marriott's answer to Starwood's W hotels but done in a slightly more luxurious and less formulaic way. These properties tend to reflect their urban neighborhoods while still providing a higher energy luxury experience. There are only a handful of Edition hotels, all located in urban neighborhoods known for high energy experiences.

W hotels are a lifestyle brand that command luxury hotel rates while offering a more specific niche experience, a combination of luxury hotel with club lounge energy and the concomitant see and be seen crowds and customer base. Lobbies are known as Living Rooms and serve as de facto social spots for not only hotel guests but the local urban denizens, too. Employees are often quite good looking, it seems. These tend to be city hotspots for bar/club activity. Design style tends to be snazzy and chic and on the minimalist edge. Definitely not to everyone's taste, but a truly unique brand that spawned a number of others (including Edition). Service levels range from excellent to curiously mediocre, with non-USA properties tending to have better service than the US properties. Some Asian Ws can offer service that is as over the top as some of the best luxury hotels, but that is not the norm. There are a few W Retreat resort properties known for offering a more consistent higher level of service in exotic locations.

JW Marriottt is what I call "safe and more affordable luxury." These are beautifully clean and nice hotels offering nice service in a modern but safe, non-edgy style comfortable style for most customers. Soft contemporary often seems to apply to the design style. Business and leisure travelers alike would appreciate these hotels. They are located in both urban centers and resort locations worldwide. There are about 100 JW Marriott properties. Service is usually quite good, but may not approach the over the top service levels of other brands due to the usually larger sizes of these hotels. While JW may appeal to more people, the average daily rate is lower than that of W, believe it or not.

There are a few Westin properties in Europe (Paris, Madrid, Venice, Florence, and Rome, in particular) that also offer luxury level service and accommodations. But most Westin hotels are only "upper upscale" and not proper luxury hotels such as those.

Westin, Le Meridien, Marriott, Renaissance, and Sheraton all occupy the same upper upscale space in terms of average daily rate. Le Méridien hotels tend to be stylish and eclectic in design, approximating a W lite approach. Westin hotels tend to be modern and clean design with a focus towards health. Marriott hotels tend to be safe and clean and more or less like JW Marriott lite...you always know what you're going to get, but it isn't standing out in any particular way. Sheraton hotels also tend to be safe and clean but have the most range of quality of all the above brands, with non-USA Sheratons being extremely good and US Sheratons often being not nearly as good or downright poor. Renaissance hotels tend to be a little more posh and reflective of locality than your average Marriott, but there's still some variety there.