I had to make the same choice with the Canon 10D & the Nikon D100. I chose the 10D & have been very happy with the camera overall. It's VERY responsive & fast, has a 8 pic buffer, controls are intuitive & properly placed. It feels rock solid in my hands (as opposed to the 300d).
In terms of the picture quality, not quite there because they generally tend to come out soft & require post-processing. From what I have seen most pictures from various types of cameras just don't have that sharpness & vivid color that you would expect. At least not consistently, it seems that the constellations must align for the right shot!
I have seen a pro photographer take pictures with a Mimaya cam with Velvia film that are just stunning. The same shots taken with a 10d just didn't have that same spunk!!!
If you have any comparison same shots of 10d & other cams, please link it will be very much appreciated!
http://www.pbase.com/fastuno