Just wondering what "Best Ending" qualifies as. is it getting the "Happy Rancher" ending scene, getting all the ending scenes (that you can get with Happy Rancher), or is it getting a 999 Ranch Master score?

Best Ending counts as the "Happy Family/Rancher" Cutscene. This is a small description of it from a very good/detailed guide: "REQUIREMENTS: Married, 2 children, 900+ happiness, 10 Power Berries eaten, 10,000 G, own 1+ cow, own 1+ chicken, hugged dog 100+ times This is the "best" ending in the game. Jack will be sitting on the front porch of his house with his wife, parents, two children, dog, and horse. They all wave at you as the screen fades. You will receive this ending even if the second child was not yet born, but your wife was pregnant with it."

999 Ranch Master Score would be the requirement for a 100% run (with the number of ending scenes being debatable).