I drive the Nikon D300 myself and have no problems in highly recommending it. There are numerous examples around from both types and ultimately it will be what you feel happy and comfortable with.
I must say that it was mentioned earlier that you need to be a photoshop professional to use Nikon. Actually these days I'm finding the reverse is true, as since going to the D300 I find I have to do less to what is coming out of the camera, and even then it is usually just a crop and straighten.
But don't forget the glass. It's the cameras combination with the lens that will decide on how your pictures look. You can have a great camera body, but if you have crappy glass then that will degrade the picture (softness, fringing etc).
It also depends on the photographer themselves. So many people lash out and buy an expensive camera and lens, then don't RTFM and use the camera to its full potential. I guess some people expect the camera to do it all for them.
The best suggestion is to do your research, and to find which camera you are most comfortable with.
Try
www.dpreview.com for a good place to start. They have reviews and forums for all the major brands and you can usually find what you want over there.
As a screener on
Jetphotos.net I have seen the best and worst of both major brands of camera. There are more factors at play than just the brand, but it's whats going to make you happy that counts.