I will be getting a DSLR soon and have narrowed it down to these two. I will be shooting car racing, motocross racing and other motorsports which on is better for this? .
If you are shooting auto racing you will likely be going for a good size lens. The cost of the lens is such that it will be the major part of the system. I'd choose the brand based on who has the best auto-racing lens.
At least I hope you are not planning to use the 18-55mm kit lens
If yuo can get up close to the track you might be able to use an 80/200 f/2.8 lens. Many people buy Nikon because Nikon's version of this lens is a great value and there are good used version of this Nikon lens available for $700 and I've seen even less.
So think ahead also to you next lens and look at the total system in your bag.
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... Both cameras have very different button layouts,.
If you pick Canon, then you wil also buy a large very expensive canon lens as is required for racing photography. Then some day you will upgrade the body of course it will need to be a Canon body.
So, don't make the dision on something as triveal as the location of a button on the first SLR body because yu are also deciding which brand next new few DSLR bodies will be. Look at the entire LINE on bodies and see if you line the the general layout of Canons or the general layout of Nikons Lok at the way each builds things.
In general what you find is the Nikon is much more conservative and sticks to what has worked while Canon is quick to jump on new technologies and ideas. One way is not best. Nikon's user interface, I think is more refined and I like Nikon's light metering best and maybe their flash system's metering too. But Canon, if you look at their lineup over the years looks best on some spec sheets. Again look at the lineup over the years NOT is one specific DSLR body, step back see big picture.
You are picking a brand yu will have to live with perhaps for 10 or more years. Switching brands is expensive most people don't do it.