June I would certainly go for Samui over Phuket. By the choice of those two locations I'm guessing you want a beach, pool and a suntan?
It sounds like you're describing the Vana Belle, which is one of the only Starwood hotels in either Samui or Phuket I've not stayed at, so you'll have to ask someone else for details
The W Koh Samui Resort is a lot of fun if you can get a good rate, but is IMHO usually severely over-priced. There is also a brand new Sheraton Koh Samui which I'm not sure if anyone here has reported on yet.