The first service retrieves just the base information of the Things related to a ThingTemplate
The second also retrieves all the Thing Properties and their Values.
So if you just need a list of the Things (Entities/Assets) and you drill down from there, use the first one because it is a lot less expensive.
If you have very static information, you can use the second one and load all necessary information at once and use SelectedRow to show the drill down (vs. something like GetProperties/GetPropertyValues based on a selected Thing)
Hope that helps.
