I have been looking into getting a pixhawk of some kind. But I am not sure which one I should be getting. What I am really asking is what are each one mainly for and what is the differences between them.
@Oscar_Wallace - I think the best place to start is with a question - what do you want to do with it? Build a copter, rover, boat or plane? You can do all these things with Ardupilot (the software), whose variants run on many different hardware platforms. Start here: http://ardupilot.org/ardupilot/index.html
Your picture represents more of a history lesson than a list of currently available products, and ultimately a very lengthy post without some idea of what you would like to do. A good place to start would be here for a listing of whats currently available: http://ardupilot.org/copter/docs/common-autopilots.html
Give us an idea of what you would like to do and we can go from there. 
r
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I want an autopilot board that will allow me to do all of them.
for a 150mm(3") copter a kakuteF7 (or mini) will do.
@wn0x. I want it to be good for all types of vehicles. But the first two that I will use it for is for a rover and then a drone.
Also I was wondering if anyone has any knowledge on the different types of ground station software and which one is good for what and why I should choose one over a different one.
I have been mainly looking at the cuav v5 nano and one of the cube boards. But wanted peoples choices on the topic.