My favorite 5-star Samui hotel with the best beach is definitely Sala Samui, super relaxing, away from all the nonsense in Chaweng and still close to everything.
Koh Samui Resort Hotel - SALA Samui Resort & Spa - Samui Luxury Hotel
The brand new W is also very cool but not as cozy as Sala Samui.
For longer stays at affordable prices, try out The Park Samui close to Choeng Mon Beach
Apartments The Park Samui - Koh Samui, Thailand - Apartments in Thailand.