I'm torn as I think giving it at the White House would be equally powerful, as it would remind all his enemies that he's still there, still in the White House.
But I do think giving the speach would be super epic, it would be off the charts to have it there, considering its history.
Compare either location with that senile prick Biden. giving his acceptance speach from his basement.
Think of it in terms of a chess move by The Donald.
Initially he announced he would give his acceptance speech at the White House. He received a lot of criticism from the Dims. "No, you can't have it there! That would be politicising the office!"
So, he counters with, "OK, I will have it at either the White House or Gettysburg." So, when the Dims push back on Gettysburg it draws attention to "Lincoln" - "Republican" - "Gettysburg Address" - "Freed the slaves."