Coin & Snow are two sides of the same coin (probably why the author chose the name "Coin"). Had Coin ruled, nothing would have changed for the districts. There would have been no freedom & no elections. Killing Snow was for Panems past & ultimately pointless had Coin ruled. Killing Coin gave Panem a future.
Actually when I was reading and I was at the part when Katniss was going to execute Snow and she was worrying about the only 1 arrow... I knew exactly she will kill Coin instead of Snow. And of course she was right. At that pont I didn't even care about Snow because he was already dead for all of the people of Panem. He was just that sad sick old man without any power. But who would be better president... I have no idea I couldn't chose. Paylor was a good choice.