PlayMaker is a Finite State Machine with a visual editor. It is the first plug-in you should get because you act quickly create behaviors wit the visual editor and the action browsers introduces you to all the power of Unity quickly.
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Pro Easy to use
You'll need to put more time in learning Unity + Playmaker compared to something like GameSalad. But once get hang of it and familiarize yourself with it's possibilities. It's quite easy to use.
Pro Elegant state-based visual scripting
Instead of a single "if this then that" event list which can become very cluttered beyond the most basic behaviors, PlayMaker gives each object a list of states where only certain events are triggered, and performing an action also changes state.
This allows for a clean, simple visual representation which helps break complex logical structures into smaller pieces, making them easier to understand.
Pro Third party plugins support
A lot of third party plugins have support for Playmaker. Playmaker team also invest time to add support for a lot of third party plugins.
It basically can do same things as scripting in Unity.
Con Limited tutorials
There are not a lot videos with Playmaker tutorials. Official text tutorials are also quite limited. Even not every action has a description on an official wiki.