Cruise line suggestions

My wife wants to take a week-long cruise around March, and the Caribbean (unsure yet whether western or eastern part) looks most feasible for us. I am not completely thrilled with the idea, due to a propensity for sea sickness (though I have not been on a large ship) and an idea I would not like the crowds and organized activities or some lines, but am willing to go along with her idea. She has already said she does not want to take a Carnival line cruise, due to a bad experience a friend had. Just anecdotal evidence, but from what I have read so far, Carnival is one of the mid-range lines, with large crowds and not the fanciest rooms. Doubt we would splurge for Cunard, but Celebrity and Holland-America, and perhaps Norwegian or Costa, sound like they may be a bit better than average. I think we would go for a balcony/veranda room if possible. Any suggestions of specific lines, even specific ships?