The Nikon D90 was the first DSLR to include a HD movie capability. It's an exceptional camera, but I find it hard to recommend it. Why? Simply because by today's standards, it is an old camera, and has been eclipsed by the newer Nikon D7000. So, unless you can get the D90 at an attractive price, get the D7000.
Suitability for Travel: Rates a 4 out of 5. While image quality and flexibility are unsurpassed, DSLRs in general, even light weight ones are just a bit cumbersome to travel with. They often require dedicated camera bags, especially if you take a lot of extras; such as lenses and accessories.
Overview: Perhaps too much emphasis has been placed on the MegaPixel count for digital cameras, as there are many other factors that determine how good the camera is. However, one thing is certain, a 12MegaPixel DSLR will perform remarkably better than a 12MegaPixel "Point-and-shoot" (compact) camera. The reason for this is the image sensor on a DSLR is larger. The larger the sensor, the less noise you will get. Noise is an unwanted grainy-looking texture in photographs, especially those that are taken at high ISO settings.
The photos shown below were taken in low-light with high ISO settings. They clearly show the unwanted noise pattern as the result of a high ISO setting. While the more expensive the camera, generally the better the noise reduction, DSLRs have remarkably improved in recent years, and even the entry-level cameras can exceed what older pro cameras could achieve.
The left photo was taken by my older Nikon D70 DSLR, which is a 2004 vintage camera, and the high ISO noise is more apparent. The right photo was with my newer Nikon D90 DSLR, which shows much improved noise rejection.
Why Nikon? Actually, I started out with a film SLR in the late '70s with a Canon FTb. In those days, Nikon was known as the best, but they were significantly more expensive than Canon. Then when auto exposure cameras came to market, Canon changed their FD lens mount, and overnight, none of the lenses I had would work on a newer camera. In those days, Zoom lenses were rare, so it was not untypical to have several fixed focal length lenses in your camera bag.
I remembered an ad that Nikon had during that time. While I am paraphrasing a bit (I cannot remember exactly what it said);
How true that statement was for my lens situation. I then found out that Nikon did not change their mount system, and even today that is true. You can mount a 50 yr old Nikon lens on a new Nikon DSLR and it will still work. Of course, you may not have auto focus or some of the other advanced features if the lens does not feature them, and you may have to shoot with Manual exposure, but most lenses will work. For that reason, I changed equipment brands and went with Nikon.
When you buy a DSLR, you are not just buying a camera, you are buying into a system - which includes lenses, speedlights, and other items. Look to the future. Most amateur photographers cannot afford to purchase all of their desired lenses at once, but rather budget a lens purchase every now and then. Owning equipment - especially lenses that do not become obsolete is the key.
However, today, Canon still makes good equipment, and is worth your consideration. You can't go wrong with either brand.
Nikon DSLR Hierarchy
Entry Level vs. Advanced Amateur: One cannot review Nikon DSLRs without mentioning a major difference between advanced amateur and entry level cameras. The entry level cameras lack the following features that - if important to you - you may wish to consider purchasing an advanced amateur camera:
Summary: You choice of the camera you wish to use is as much a matter of your pocket book than anything else. A good photograph can be taken with an inexpensive camera, and a lousy photo can be taken with an expensive camera. For some folks just starting out, the entry-level D3100 presents tremendous value, and there is an in-camera help system that may prove to be indispensible. The entry-level cameras even often find their way into professional photographer's bags as a second camera as they are often light weight, easier to setup and use, and if they are lost or stolen, its not as expensive. Often its better to have a camera that is easy to use as you can concentrate on taking the photo rather than setting the camera up. However, the chief advantage of the more expensive camera is flexibility, and the ability to operate in the fringe environment (low light, dusty or wet conditions, and so on).
Remember the theme of this review is the selection of a camera that you may want to take with you on a cruise. You don't want to lug a heavy, super-expensive pro camera with you, so cameras in the D3100 to D7000 range will provide satisfactory performance in the cruise ship setting, yet not be too heavy to carry.