I have a Canon Digital Rebel XTi. My husband bought it for me as a birthday present. I have been thinking of trying my hand at sports photography. For now, though, I'm practicing with puppy photography... both have lots of running.
Anyways, I love it! Picture quality is great, and the settings are very user-friendly. I had most of it figured out pretty quickly. I'm still not the greatest at actually composing shots, but it feels good to use and I get some really nice photos out of it. (A few of them are importing to my computer right now, actually...
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I have never tried a Nikon DSLR, so I don't know much about them. We have a Nikon P&S that takes pretty good photos when I don't want to haul the Canon around... but that isn't very often anymore.