what is the difference between the different ending save file transfers?
The startersave is for people who have already played most of the game so they can get to the most recent content pack quickly. The DataCrystal transfers some extra information from the original game. At this time, it only unlocks one additional scene, but other information is carried over as well, and it will be used more in future chapters.
The scene in GT that the DataCrystal file unlocks is unlocked based on number of defeats in the first game. Low defeats mean no scene, mid means a scene, but you can fight to avoid it, high mean the scene is forced. Any ending in the first game where Mezz leaves the island will write the file with the relevant information. The other information in the file is not currently used, but will be later.