We went to Huatulco (Mex) a couple of months ago.... Not a very big place, and definitely not a party hub. I found it pretty relaxing, and the hotel was nice (Barcelo)...went with Signature vacations and it was ok. There are other resorts around there as well, but here's some info from Sig vacations:
http://www.signaturevacations.com/huatulco