I went to Belize in 1967 when it was British Honduras and hadn't developed a tourist industry. I finally returned last year and found that the town of Belize City still looked the same but the people had developed a lot of the huckster traits found in other tourist areas. It is an interesting place but you won't find much nightlife.
Jamaica is a country that I have no desire to see again. The natives weren't friendly; in fact they were often insulting. We were going to stay two weeks but left after a few days.
I haven't been to Costa Rica for some time but it was definitely a place that is worth a visit--beautiful scenery, stable government, and friendly people.
I still like Mexico the best for a beach resort. Playa del Carmen (45 minutes south of Cancun) has great beaches and is less expensive that Cancun. Isla Mujeres is probably one of the most exotic tropical islands I have seen. Cozumel is great for snorkeling and scuba diving, but the beaches are not very good.
Since you like water sports, beaches, historical things and nightlife I would suggest one of the all-inclusives in Playa del Carmen. Great beaches, shows and discos at the resorts, proximity to Tulum, Coba, and other Mayan ruins. Check out the Iberostar resorts in that area.