What should i buy for my First DSLR Camera? Nikon vs. Canon?

I am thinking about buying my first DSLR Camera, Should I choose Nikon or Canon?
Nikon D3100 or D5000 or I also thinink about Canon 550D. I don't know what to chose.
Any other brand suggestion aside from N and C? My budgest is not more than 1000USD.
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