2D Toolkit provides a completely proprietary sprite implementation. Though it can be used alongside Unity's 2D systems, the two are completely separate and require different code to utilize.
Tiled will automatically create borders for different terrain types set up by the user. Has some setup time to get things working but helps in the mapping process.
AutoTileSet is a tile placing tool part of the AutoTileGen family that is supported in Unity, Construct 2, and GameMaker to create tilemaps. AutoTileSet does not need AutoTileGen to work.
While placing tiles on the tilemap AutoTileSet will place appropriate borders and filler tiles instead of the user having to change each tile for each variation. It also support multiple tile sheets for variation and placing them correctly.