I stand corrected , a quick search revealed it to be more than 300km closer than Honolulu. It is warmer in summer, but the op was talking about winter, for which I find the temp in Honolulu to be more comfortable.

I would also recommend staying away from the Chinese tourist horde (although I am ethically Chinese myself), as they tend to push prices etc up and tend to help create a chaotic atmosphere.

I would also recommend going to some out of the way places on Hainan Island instead of spending all your time in Sanya (there are less buildup parts of Sanya, but I think if you re after a bit local culture, venturing a bit further our can help). renting a car (look out for mileage limits on Chinese car rentals) or taking the train from Sanya to Haikou and stopping off on the way etc.

All in all I much prefer Hawaii over Sanya (as do the people I know who have been to both places), but I would take Sanya over greenwich London (where I am now), anyday.

Also thanks for the message corporate wage slave, it is nice to be welcomed!