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 two newer Nikon cameras, the D7000 and D3100. So, unless you can get the D90 at an attractive price, pick either D7000 or D3100 depending on how much cash you want to lay out. The D3100 is considered an entry-level camera, while the D7000 is considered an advanced-amateur camera.
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.
Nikon D70 @ High ISO - Martin B-10 Bomber, USAF Museum - Wright-Patterson AFB, OH
Nikon D90 @ High ISO - Martin B-10 Bomber, USAF Museum - Wright-Patterson AFB, OH
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 lens mount, and none of the lenses I had would fit. 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), "The photo equipment you don't have to replace is the least expensive, no matter how much it cost". 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 40 old lens on a new Nikon and it will still work. Of course, you won't have auto focus or some of the other advanced features, 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.
However, today, Canon still makes good equipment, and is worth your consideration. You can't go wrong with either brand.
Raw photos vs. JPG, which one? The primary difference is that JPGs are highly compressed photos, which allow more photos to be saved to a memory card. If you look at a JPG photo with a critical eye, you can usually see artifacts as the result of the compression. Raw photos, on the other hand are not compressed. This results in a higher quality photo, but it results in a larger file size, so not as many photos can be saved to a card. However, this is not as much of a problem these days as memory cards are cheap. But Raw photos are proprietary formats, so they usually must be converted to a JPG or other format before they can be printed or viewed on a website. However, many of today's photo-processing software can read Raw files from most manufacturers.
If you never intend to retouch your photos, you can shoot JPG. However, JPGs are lousy when post-processing as the critical information is gone. Any attempt to retouch a JPG will result in mush. Some professional photographers insist that every photo needs to be retouched, or at least sharpened. I'll leave that up to you, but perhaps one good alternative is to use the JPG+RAW mode that Nikon DSLRs have. This actually results in two photos per shot; one saved in RAW, and one saved in JPG format. This is probably the best of both worlds as you have a RAW photo should you decide to retouch it. Shooting RAW will also allow you to extend your low-light shooting a bit, as you may be able to correct a moderately underexposed photo.
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 indespensible. The entry-level cameras even often find their way into professional photographer's bags 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.