I prefer Canon probably out of habit. Canon has had quite a reputation for making high quality digital imaging products for probably the longest time. But Nikon has been gaining speed and makes excellent cameras as well. I'm not sure you will be able to find a clear answer to this discussion.
I would say both brands are generally similar.
It is said that Canon produces natural colors while Nikon produces sharp colors.
But in fact when you employ post-processing, the difference could be ignored.
As a Canon 400D user, I would recommend Canon to you.
Of course now you can get a 450D and the new Canon EF-S 18-55 mm IS and 55-250 mm IS to start with.
If you want to shoot sports and low light, go Nikon.
If you want to do more commercial photography, go Canon.
If you want smaller lenses and bodies and like shooting subjects far away such as wildlife or birds, go Olympus.
Or better yet, forget all that and go to the store, feel out the cameras that have the features you want in the price range you want (be sure to check out the prices of lenses and other accessories as well) and pick the one that feels best to you. Check out their layouts and the menus and how they feel in your hands. If you have the option, rent one or more ant try them out for a bit. In the end, there is no best camera or brand. The best one for you is the one you are most comfortable with. It's the photographer, not the camera, that takes the picture.
They are both good in their own ways. You can never go worng with Either brand and you have to remember that the lenses are not cross-changeable. Like Cliff said.. go to the local store, feel the cameras in your hand..
I am buying a Nikon D300 and from the trials the difference between Canon and Nikon is very little. I was all for the Canon 40D but once I held it and played with it I did not like it . I tried some other up market ones and I liked the Nikon best. But it is a matter of how it feels in your hands and whether you find it easy for you. I would suggest you go to the shop and try them. Cliff is right. The best one for you is the one you are most comfortable with. Janies also right feel the cameras in your hand.
You're welcome:) make sure to check out the new Olympus and Sony dSLRs. They're good too. You can use Minolta lenses for the Sony and they're really good and cheap. But IMO Pentax K20D would be the best choice because of its functionality and price:)
One thing needs to be mentioned here when buying a new camera especially if you are going to be spending a couple of thousand Dollars. If you have a particular system i.e. Canon or Nikon or any of the others, it is a logical thing to stick with the same system that you started out with, that is if you already have a DSLR with one or more lenses. You will probably find that the lenses from your earlier model camera are compatible for the later model you are buying. If you are buying your first DSLR, then this will not matter.
The most important thing to remember is not to try and go for the more megapixel hype, but to get a camera with an exceptional image sensor and really good lenses. Unfortunately, Canon's entry level cameras, 350D, 400D come out with really mediocre kit lenses, but one can get something better if you are prepared to spend more. It all comes down to how much money can you afford. My suggestion is that you choose your camera with all the above info already said, but find out how good the sensor is and the lense you are getting with the camera, because the kit lense could make you very dissatisfied with your images.
So remember, it is not about megapixels as much as it is about lense and sensor.
Hope this helps people understand what they need to look for.
I'm a Canon shooter. I love the quality of their products and how long they have been around.
I have also shot Nikon. It seems to me that you can get a better image quality camera with nice lenses when you go Nikon, for a more affordable price. But if you are planning on stepping up with the big dogs and emptying out your wallet, Canon to me is the way to go. They are what you see on all the NFL sidelines shooting the players. Or at a golf tournament shooting Tiger Woods. Mostly all white lenses, which means Canon.....
Either way it is a personal preference and I don't think you will be un-happy with either one you choose. Nikon and Canon are most definitely the 2 big dogs when it comes to cameras....
I don't think you'd be disappointed with any DSLR that you buy, but I would highly recommend going to the store and putting them all in your hand and playing around with them for a bit. Nikon, Canon, Sony, Pentax and Olympus all make great cameras.