I seem to own almost all of the currently available 2D solutions 
so, here’s a short review comparison
Sprite Manager 2
used to be the only one available, so if you compare it with no 2D at all (the way it started), it was amazing, but now with the competition, it doesn’t really live up to its name or price range.
I use it only (nowadays) when I use EzGui to have maximum compatibility between them.
2D toolkit
has amazing unique features like
- dicing big images into smaller ones to fit as many images as possible within 1 texture
- setting the colliders in a visual editor you’re no longer restricted to Unity’s basic colliders
the problem with it is in the (not so) friendly way of making animations, everything is done using drop down lists, from setting the number of frames in your animation to making the animation itself
(for each frame, you have to scroll down the drop down menu select the image you want for that frame)
ex2D
the most user friendly, you just have to set everything (the atlases) once, after that you drag drop your own images, if you know how to use Unity, there really isn’t much more to learn before starting with it,
also, it really excels in the animations, it allows you to set a certain frame to take stay for longer or less time (think about timing a swordsman preparing his attack (longer time) then cutting (shorter time)),
also, it allows you to put events on the timeline for the animation (again, for the swordsman, when do you want to check for collision, set it as an event in the editor at the precise moment).
by far, my favorite for sprite based animations.
the previous 3 are all for sprite based animations.
the next 2 are for cut-out or bones-based (skeletal) animations (you can notice that I’m not an animator therefore not sure which is the correct term for these packages)
they both support changing the location/scale/rotation the texture of each bone at any time (key frame) in the animation.
they can help you save a ton of memory for the animations. (you only need the basic sprites of the character you want to animate not a sprite for each frame)
Easymotion:
Has its own workflow that’s completely different than unity (e.g. Z-index doesn’t exist !! use the plugin’s own depth variable),
also, it has its own shaders (didn’t really try to change them)
I haven’t checked really, but I think there’s a component that allows you to overcome this. (but it’s not the default)
you cannot control the speed at which it arrives at a key frame (easing in or just arriving fast)
a little tedious to change the pivot for each image
but, it allows for events to be called inside the animation it’s very easy to make sprite-based animations inside it
the developer said he’ll include a collider-per bone in a release (not really sure if it was released already)
Smoothmoves:
integrates well with Unity’s workflow
allows you to choose your own shaders ( recommends Particles/Alpha blended which is supposedly very fast)
allows you to change the curves of the keyframes (giving you control over easing in/out or moving fast)
allows you to change the pivot point while animating (in fact, it allows you to have different pivot points for each key frame)
but, the triggers are generic, so you have to write a script to call the appropriate function at the appropriate time,
making sprite-based animations is still a little rusty, but it’s getting better with each release
allows you to have a collider per bone to activate it/deactivate it during the animation
allows blending the animations inside the editor
to be honest, I might be a little excited about Smoothmoves cause it’s the latest plugin I bought the one I’m currently using,
but all of the info I provided are true to the best of my knowledge, I might have forgot something that would make some of the plugins seem a better/worse choice, but these are the main points I got off my head without re-trying everyone of them again.
about UMotion 2d, it seems like a new plugin that’s not released yet, I haven’t really looked at their videos so far.
also, I haven’t tested Orthello or Rage tools
(but the developer of Rage Spline is making a new plugin that’s pixel-based if you want to follow up on it)
after effects, toon boom anime studio are different tools they probably can be used to create sprite-based animations that can be used with any of these plugins
