Ardyn was good. I liked that his motivation was very personal and he played the long con. I wish he got a bit more development as the game progressed rather than an info dump near the end, or that you didn't need to rely on add-ons and other media to find out more about him. As FF villains go, I agree he's in the top 5, but that's not saying much as this series has things like clouds of evil for villains.