Actually we are surprrisingly unfanboyish about PlayMaker here I think. Just looking through the posts here you'll probably see some people noticing missing things and all, but all in all PlayMaker is just so stable that noone can really complain much.
1) Yes, PlayMaker works with Unity 4.0 indie, although it does not yet support many of the unity 4.0 features, as a large number of the userbase are still using 3.5 . If you decide on PlayMaker, I can help you write custom actions to remedy that though
. All actions are kinda open source, although they have a big copyright by Hutonggames in it
2) Yes, it's probably one of PlayMakers strengths. A lot of people pass messages and variables between scripts and FSMs all the time. You can also Set and Get Properties from scripts, which lets you choose from an automatically generated list which variable you want to get or set. Really awesome if you aren't familiar with a script, as it will also return inherited variables etc.
3) PlayMaker ends where the Unity GUI does. This means natively there are no ways to work with lists, arrays/hashtables, dictionaries, enums and private object classes. For lists and dictionaries we have a plugin called ArrayMaker, which extends Unities capacities by offering components which each contain a list or dictionary and can be accessed by playmaker as wel as changed via the GUI.
So effectively the biggest concerns are the object classes and enums. There are ways to get around enums by converting them to strings, but as for object variables, we can only access a few directly. This is why many plugins, such as A* or the like, need custom actions to work with. If you know how to program, then there should be no problem though.
I asked myself the same questions as you did, and seriously, there's not much of a difference between the FSMs here. PlayMaker just felt the most complete to me so I chose it. Future updates focus rather on core funcitonality than new actions, which I appreciate very much as we ourselves can write most actions without problems ourselves.
If you plan to use PlayMaker on top of your normal scripts then I think this is a great choice. However, if you want to use PlayMaker all on its' own for a huge game project, you will see that the GUI reaches its' limit after so many FSMs and states. It slows down a lot after a hundred or more states in one FSM. I doubt Antares or uScript would do any better in that situation though, but I can't be sure.
To not finish this post with a negative point...ehhh PlayMaker is great! really really great
Nice community, the next update is tremendously exciting still and the ease of extending PlayMaker is just awesome