Onlyme
I looked at all of the above destinations for a 7 day break in April. Koh Samui won in the end as it's only a 3 hour direct flight from HK.
Good luck
go to perhentian island in malaysia.
i went there last month, it was so beautiful.
you can do all sorta activities like snorkeling, massage.
it's not pricey to stay in resort but no direct flight there.
I just got back from Li River Retreat in Yangshou. It is laid back and slow paced, just ride bikes around the country side. We have a 5 year old and a 1 yr old and getting out of the city was a nice change. There isn't a beach, but the food was good and the staff is great. I went to a cooking school and the family went bamboo rafting. check out www.yangers.com