I would go for Celebrity if you want a touch of class - at that time her brand new 'Solstice' will be in the Caribbean. Try that.
Whilst the Solstice starts its first cruise in December this year its sister ship Equinox will also be in the Caribbean, just one upmanship as it only starts cruising in August 2009 with the following itenerary: Fort Lauderdale, Florida, George Town, Grand Cayman, Cartagena, Colombia, Colon, Panama, Puerto Limon, Costa Rica, Roatan, Honduras, Cozumel, Mexico, Fort Lauderdale, Florida, but as a.n. says Celeb are a bit more upmarket than P&O but sure you would enjoy either ship. Give 0800 091 1629 and speak to their cruise department, it costs nothing to ask them this site is their companies.
P&O will have Oceana in that area and it is a family ship you would fly Charter there and back,RCI has more family ships and a bigger choice of ships and Celebrity is a better class of ship but are family ships,the problem with the last 2 is US customs which can be a pain to get through.Best of .luck .