Welcome to ScubaBoard! As a new certified diver you can choose from a lot of resort dive locations. Just tell your dive op your experience level. The choice between Roatan and Bonaire is a close call. I would recomend Bonaire because the diving is usually from shore, while the best diving in Roatan is from boats. Why recommend Bonaire, you can go with a guide, or go with divers you meet at the shop. A rental car opens up half the island with park and dive. The water is warm, current is mild and in most places you can dive shallow depths and see lots of fish and coral.
At the bottom of each page there is a box called "Forum Jump" Look up "Greater Caribbean" forum and you can read what the divers are doing today. Use the search function and you can look up messages from the past.