The Naka Island, a Luxury Collection Resort & Spa, Phuket:
We enjoy a great beach for swimming and snorkeling: Beach looks nice but when tide is low you cannot swimm. Snorkeling useless (you don't see anything)
Very clean and modern hotel: Clean yes, modern not really. I had an Pool Seaview Villa and was really disappointed. It looks so nice on pictures but in real they are not.
Good food: nope, you can eat but it is not delicious (and for that taste totaly overpriced)
Romantic and relaxing: YES, I think thats why this property still exists. The surounding is really beautful, as you are nearly alone on the island and the beach is private.
JW MARRIOTT KHAO LAK RESORT & SPA:
We enjoy a great beach for swimming and snorkeling: Swimming yes (but it can have strong current and big waves) Snorkeling useless (you don't see anything) but from there it is not far to Similan Island where snorkeling is fantastic.
Very clean and modern hotel: Clean yes, modern not really. Typically JW style, a lot of dark wood. I would not call it modern and the hotel is outdated in my opinion.
Good food: nope, you can eat but it is not delicious
Romantic and relaxing: No, it is an huge resort with many tour operator tourits.
The only alternative I could recommend would be the Renaissance Phuket.
We enjoy a great beach for swimming and snorkeling: Beach is nice, long, lonely, no people but swimming can be hard (I was the only person who try go swimming) really big waves and really strong current!
Very clean and modern hotel: YES, everything is clean, fresh and modern.
Good food: YES, very delicious (it is so delicious that when I stayed last time at JW Phuket I drived to Renaissance to eat there instead of eating at JW)
Romantic and relaxing: YES it is an small resort, the Pool Villas are really private (nobody can look into your area, at Naka Island people may look into your area) and 10 times better than the Naka Island Villas even when it is a lot smaller.