Re: Nikon D200 or Canon 20D
the D200 is much newer than the 20D and is really a camera in a class of its own . People call it the 'baby D2X' for some very good reasons. The 20D is already out of production- it was discontinued almost 18 months ago and replaced with the 30D which by Canon's release history is due for replacement any day now.
Even thougn thr 30D is slightly cheaper, the D200 is still just about the best bang for your buck out there. Do you have any gear from either brand?
Look through the viewfinder
Just take a look through the viewfinder on both cameras. The D200 has a proper pentaprism giving a nice big image. The 20D is like looking through a keyhole.
I'm surprised you compare the two. The 20D should be much cheaper as it's been out of production for a while. Lots of people have made lots of great images with this camera so it should really be a bargain.