When comparing 2D Toolkit vs Unity Sprite Packer, the Slant community recommends 2D Toolkit for most people. In the question“What are the best tools to create sprite atlases for Unity 2D?” 2D Toolkit is ranked 2nd while Unity Sprite Packer is ranked 4th. The most important reason people chose 2D Toolkit is:
The documentation for the toolkit is well written and there are video tutorials as well as an active community.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Good documentation
The documentation for the toolkit is well written and there are video tutorials as well as an active community.
Pro Includes source code
No need to pay more to get access to the source code.
Pro Pixel-perfect camera
Pixel games in the style of 8 or 16 bit systems need to have each pixel uniform on the screen which 2D Toolkit supports with a camera component.
Pro Add colliders in the atlas editor
Choose from either a box, sphere, or mesh collider that will output as either a 3D or 2D collider in Unity.
Pro Create different resolutions of atlas
2D Toolkit allows for different sizes of atlas from 1x, 2x, or 4x which can be changed depending on platform resolution.

Pro Built to work inside Unity
2D Toolkit is an editor extension so users don’t have to leave the Unity engine for tile mapping.

Pro Create Atlases within the tool
Create sprite sheets for tiles to save draw calls and to keep tilesets organized.

Pro Supports the Tiled TMX Format
Create tilemaps in Tiled and implement with 2D Toolkit.
Pro Create Custom Output Via Code
Set custom packing specified by code useful for those who have to follow a guideline on packed sprites.

Pro Comes built into Unity
The Pro license brings full 2D support within Unity without having to use an external program or plugin for creating atlases.
Cons

Con Doesn't integrate with Unity's Sprite system
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.
Con Doesn't work anymore
As of Unity 2017 it's completely broken.
