I think the "correct" answer would be the D300, if you are simply comparing the list of features.
I came to digital photography late (real late) and my experience prior to the D200 was a simple point and shoot. I was driven to digital by the crappy quality of local film processors. I ended up buying a D200 because 1) it was relatively cheap; 2) It could operate well with my collection of MF Nikkor lenses. I also rationalized that if I liked digital photography that it would make a good second body for a D300/S outfit.
The D200 has exceeded my expectations. It has a nice heft, the controls are solid, the metering is spot-on and the images are outstanding. I used the difference in cost (compared to a D300) to upgrade the tripod head to an Arca-Swiss monoball. I might buy a fancier body someday (D300S? D400?) but I don't feel that I'm limited by my gear (talent yes, gear, no).
I tend to use a monopod or tripod, and keep the ISO at a lower level. If you shoot a lot in low-light conditions, you would probably be happier with a D300.
A feature I think I would enjoy on the newer bodies is LiveView, since I do a lot of macro work.
Your fellow Nikonians ar not very happy with the MB-200 grip, which might be an issue for you.
I purchased A RRS L-plate for the D200. The plate is not compatible with the D300, and these babies are not cheap,even used.
Can you buy the D200 with the caveat that you have X days to try it out, and exchange for the D300 if it is not satisfactory?
You should run the bodies through the "Buying a used body" checklist pinned above, to make sure they are completely functional.
"It is not death that a man should fear, but he should fear never beginning to live."