Not sure if I can only choose one otherwise I would choose all three.
For selfish reasons I would choose a sequel, or an unrelated story set in the same universe. It would probably make the most sense to create a remaster so that people who missed the game or were too young for it can get in to the world before they move on to a new game in the series.
It has been quite a few years since I last beat Skies of Arcadia so I would love to see a remaster too. Even a budget remaster would be appreciated.