At the Rocky Mountain Civil War Symposium Tim Smith talked about the "Golden Age of Battlefield Preservation," that time in the 1890's when all the factors aligned for a good amount of battlefield preservation. (Review of symposium here and here, and check out Smith's The Golden Age of Battlefield Preservation : The Decade of the 1890's and the Establishment of America's First Five Military Parks and A Chickamauga Memorial: The Establishment of America’s First Civil War National Military Park for more information).
The next big wave of preservation would not happen until the 1920s when several other battlefields were preserved on a much smaller scale. These parks were much smaller because of the financial cost involved and also because urbanization had often covered much of the battlefield. That is why we do not have a Stones River, Franklin or Atlanta battlefield park preserved on the scale of Chickamauga. In the 1890's Congress had other opportunities but for a variety of factors they ended up creating those five big parks (Chickamauga-Chattanooga, Shiloh, Vicksburg, Antietam and Gettysburg). And they did study to some degree creating other parks, I forget how many Tim said, but I think it was nearly two dozen battlefields.
That got me to thinking, if the veterans had been able to preserve one more battlefield in the 1890's (and preserve it on a large scale like Chickamauga or Shiloh) which battlefield should they have preserved? I have too many options to narrow down to just one more battlefield.
Perryville is in great shape, though still not a national park, so while it would have been great if it had been preserved in the 1890's we lucked out.
If TVA had not happened then it would have been great to preserve Fort Henry. I'm not sure it would add a whole lot to the story but it still feels weird that a battlefield is now at the bottom of a lake. Of course if it had been preserved then TVA would have faced another obstacle and might not have happened. In the course of American history the creation of TVA is probably more important than preserving a single fort (unless that fort had a huge impact on history, Fort Henry while important was not a supremely important event).
I would like if there was more ground at Corinth and Iuka to study but those were not huge battles. I think a sixth park should have been a large battle.
I'm not sure how you preserve Atlanta. There are three battles for the city but none of those are the final word on the fate of the city. Plus they are spread out. The same goes for the other battles of the Georgia campaign. While I would love if every one was preserved none are really that huge battle that cries out for total preservation.
Its a shame how little of Franklin is preserved and I would love for it have been the sixth one in the 1890's. It would also have preserved an 1864 field so that, in theory, the visitor centers could have worked together to tell the entire story of the war. I think it should have been the sixth large battlefield.
My other choice for the sixth large battlefield is Stones River, and the two are very close in my mind. I think I'd give the edge to Franklin only because it would provide an excellent chance to link the story of the war across the battlefields, and being in 1864 it would help bring to a close the war. People could do a loop going from Shiloh to Vicksburg to Chickamauga, and Chattanooga) and end up at Franklin. A one week vacation/pilgrimage could tell the story of most of the war. But if not Franklin then I think it should have been Stones River. I think Stones River is an interesting battle to study, lots of maneuver and fighting, and only a small portion is saved. I heard a ranger there once say that if he had been forced to only save 10% of the battlefield this is the 10% he would have picked, and while the 10% saved might be an important 10% there is so much more to this battlefield that has disappeared since the 1890's.