Caribbean in August is a bad idea due to hurricane season.
Depends which part of Caribbean - hurrican season used to be July - Oct, now seems to be April - Nov! I would think twice about going in August. Lots do I know, but there is always that risk. What Cruise Line depends on what you want - 4-5 star food, accommodation, Casual or formal.Most of the American style, such as Celebrity RCI Princess NCL have all that. NCL is lmore casual- dine when you want. But the others have flexibility. The other consideration is activities and entertainment. The ships are getting bigger and bigger with ice rinks, golf, bowling, etc. etc. If you want just a quiet cruise with no such activities you are better going for a slightly smaller ship on which there will still be plenty to do and all the luxury, Or if you don't want anything like that at all then there is the Fred Olsen type cruise where the most strenuous activity will be a dance. If you want the sun and to be able to sunbathe make sure the ship has plenty of deck space, some don't have wrap around decks and you can only sunbathe on sun decks (small and crowded) or round the pool (can get noisy ) There are so many conflicting views shown in some of the reviews its best to read as many as possible about the ship you are considering and take into consideration the ages and experiences of the people making the review to guage what is probably going to be best for you. A good agent (like Cruise Co) will be able to guide you if you tell them what you expect from a holiday. Good Luck.