I’ve read that embedded tilesets are a legacy thing and will be deprecated in future releases. On the other topic of tileSetimages vs collections, collections aren’t sortable atm, only via image order and editing the tsx file.
I think the main benefit of external tilesets is the fact they can be shared between maps. When it comes to a single image versus a collection I believe it’s more of a personal preference. Separate images may also be more convenient as tiles get larger.
Using a collection, it can be easier to add/remove tiles from your tileset and it allows using tiles of different sizes. But indeed, the ability to rearrange and sort/search the tiles in a collection is still missing. Also, I would like to support tiles of different sizes also for tilesheets.
Embedding tilesets may simplify distribution and/or your loading code. As an export option I don’t consider it deprecated, but I see no benefits of using embedded tilesets while editing maps.