[me_dennis]

I just came back from a Eastern Caribbean cruise (Miami, St. Thomas, Tortola, Nassau) with NCL Getaway.

Here are a few tips:
I booked with Expedia.ca about 1.5-2 months before the sail date. When you book through Expedia, someone from the Expedia Cruiseship Center calls you and help you out with any questions you may have.The Expedia Cruiseship centre agents are extremely helpful. They print everything off for you in a little package, including the itineraries, all customs forms, premarked luggage tags (which makes embarkation super easy), and even the liquids ziplock bags for customs.
Unfortunately, when I booked my cruise, there weren't much for promotions. Usually you can get some promotions where you can get a few hundred dollars in room credits to use towards anything on the ship (including the $12-15/person/day gratuity fee, drinks, restaurants, excursions, etc).

From our limited experience, we liked Royal Caribbean the best in terms of overall satisfaction. The service was fantastic, the food was good, and the ship was overall pretty nice. With Norwegian, the ship we sailed on was a newer ship (Getaway, built in 2014), so the ship itself was very nice, but in terms of service, we found that the staff were not as friendly or helpful as RCI. Also, we found that NCL really nickle and dimes guests with a lot of hidden extra charges and fees. For example, you cannot refill water bottles on the ship for health reasons, and so you have option to buy bottled water. What they don't tell you is that everything you buy on the ship (including water, drinks, items from the gift shop, snacks) have a hidden 18% "gratuity and service fee". I didn't like this very much as I felt like there were a lot of added extra costs. It may be the time of year that I cruised on, but I found NCL to be very family friendly. There is a huge waterpark for young kids, and a really fun waterslide for both adults and kids.

Carnival has older ships, and is generally a younger, party crowd. I've heard that Carnival's main dining room usually serves lobster, where the other 2 I mention do not.
Carnival is also generally cheaper too, and they have their own private island in the Caribbean which is usually one of the stops.

I've also used vacationstogo.com in the past. They are pretty good for last minute deals, and you can sort by departure port, or destination (ports of call), as well as month, length, cruise line, etc.

As for times of year, you want to avoid the hurricane season (July-September), which should be fine if you're looking at March. As someone mentioned, Easter would be pretty busy with kids being on spring break, but if you don't mind the children and crowds, it should be fine.

My next cruise will be with Disney Cruise Lines. I have heard nothing but good things about it, and everything Disney does is top quality. Plus their private island, Castaway Cay, looks fantastic.