We spent three nights at Amanpuri and thereafter 8 nights at Trisara. My trip report was linked to earlier in this tread. I loved both for different reasons and could have spent more time at both of them. Stay at both of them - I would not choose just one. Especially if it is your honeymoon, I would not do too much travelling to other parts of Thailand, rather go on one or more excursions from Trisara or Amanpuri or go out for dinner a night or two if you feel like it (no need to leave the wonderful resorts, but it is an option better than moving around too much, I think). If you decide to combine Phuket with one more destination, I would go to Bangkok, and do it at the end of the honeymoon (too tired at the beginning) to see the wonderful temples, do some shopping, have great food and enjoy this exciting city. I would stay at the Siam in Bangkok which looks stunning and where you get the resort feel even if you are in a big city or - obviously - the Pen (where we stayed) or Oriental.