FWIW, here's what Marriott's Premium Brands say that their competitors are:

Autograph Collection:
TARGET COMPETITORS

• Curio by Hilton
• Leading Hotels of the World
• Preferred Hotels
• Small Luxury Hotels

Delta:
TARGET COMPETITORS

• DoubleTree by Hilton
• Crowne Plaza

Le Meridian:
TARGET COMPETITORS

• Hilton
• Intercontinental
• Kimpton
• Loews
• Hyatt Regency

Renaissance:
TARGET COMPETITORS

• Independent/Boutiques
• Kimpton
• Intercontinental

Sheraton:
Target Competitors

• Hilton
• Hyatt

Tribute Portfolio:
Target Competitors

• Curio
• Leading Hotels
• Preferred
• Independent Hotels

Westin:
TARGET COMPETITORS

• Hilton
• Hyatt

No competitors listed: Gaylord, Marriott

David