I still think Montana is the best possibility there is. Of course the whole question is a little bit of a joke. There never was a place where all the dinosaurs shown in LBT lived (not to mention that many kinds didn't live at the same time). However, bones of most of them were found in Montana. Montana is also close enough to the northern pole to allow an occassional glimpse at an Auroa Borealis (LBT 3), and even some eons ago there were some mountains that could go for some of the mountains we see in the LBT movies. Volcanic activity in those days was much stronger than it is nowadays, but even today we have Yellowstone not too far off.
There is one point in conflict with the Antarctica theory. Of course it wasn't permanently covered in ice by that time, but they did have a kind of "annual ice age" with snow and everything. According to LBT 8 snow must be something the dinosaurs of the Great Valley really don't know about. A point supporting the Antarctica theory is that there may still be a place under the ice where fossils of all the dinosaur kinds shown in LBT can be found. But it is not likely.
