I have been several times to Bulgaria and that is something I can recommend to everybody who likes sunny holidays, for those who like partying as well as for those who prefer family holidays. Those who are interested of history will visit Nessebar or other ancient loactions. Those who prefer to meet with the nature will go to Ropotamo River Reserve or Snake Island.
Should you prefer busy resorts, bigger hotels and international society go to the north of the seaside. Sunny Beach, Golden Sands is something for you. When you prefer places with more local climate take holidays to Bulgaria in one of smaller souther resorts.
I have spent my bulgarian holidays in Sozopol which is right in the middle an offers both - busy downtown clubs and more quiet locations on the outskirts of the town.