Originally Posted by
ericbowles
There are some situations where the crop body makes sense and others where the full frame is better. It depends a bit on your lenses and what your plans are for future upgrades.
Your direct question is about how many pixels you can put on the subject, and the resulting image quality. The 1.6 crop factor is just that - a crop from the full frame image. There are advantages of a full frame camera, but only if you you can fill the frame without cropping. Once you start cropping you might as well go with the crop body since it will probably have more pixels on the subject.
Now there are situations where a full frame excels. For example, if you have enough reach, the issue becomes creating subject isolation and a smooth background. That's a lot easier with a full frame body and a longer lens. The full frame cameras also can have large pixels - which translates into better low light performance. If you photograph subjects in low light that may be more important than any other factor.
Generally the full frame lenses are heavier and more expensive. Put them on the full frame body and corners can become soft, so high end glass can be more important. The same lens on a crop body eliminates the corners allowing better image quality. On the other hand, if you need a light weight kit, a crop body with teh lighter lenses might be a better choice.
At the end of the day, I would be reluctant to go with a full frame body if you typically are cropping by 15-50%. If your lens kit provides enough reach, a two camera kit with a full frame and a crop body could make sense.