Both have good snorkeling and diving. In Belize, we have used Sea Sports for snorkel trips and they were fine. We also have walked around Belize City - seen the old Government house and museum and the Church, etc. - some people do not like walking around the City but we were comfortable enough. Roatan dive shops have limited snorkeling in our experience - you can email any of top ones - Coconut or Roatan Divers or whatever - and ask them about snorkeling opportunities for when you are there. If they do not have anything when you are there, ask for a recommendation if it is snorkeling you want. Not familiar with Roatan other than in the water.