Hi all!
This is my first ever post on the FFG forum!
Just a quick question -
My group wants to start playing the FFG Star Wars RPG. We have all three core books and want to create characters using all three books. But I was just wondering which GM kit we should get? I would guess Force and Destiny as it's the most recent but I have no experience with this system.
Thanks in advance for any responses 
Maestious
Depends what extras you'd prefer: expanded nemesis rules (EotE), rules for squad based combat (AoR) or lightsaber construction and expanded Knight level rules (F&D).
The GM screens are virtually identical, except for page number references and the weapon tables (and the art of course).
Then there's the adventures that comes with. These follow the themes of the different games, more or less.
All of them are going to include stuff not found in other books. I got all of them, as I wanted the adventures and the other information found in them. As for which for you, that depends on what kind of game you're running. If you're running for a lot of Force users, I'd go with F&D. If you're running a more Edge-style campaign, then go for Edge. If you're doing the military thing, go for Age.
I guess figure out what your players are going to make, and then, as you build the campaign around that, then you can make the decision where the focus will lie.
I have the GM kit for EotE and F&D. I don't have the kit for AoR, yet. Yet... Im noticing that the charts in the screens are almost identical, with some minor variations. The EotE screen has more weapons that a smuggler or freebooter might use (disruptors, thermal detonators, gaffi sticks, bowcasters, ect) while the F&D screen has more lightsabers and their variants (training 'saber, shoto, double 'saber). The modules are also written for that particular setting. Characters from the other settings would have fun, and the players would have a good time, but the modules in the GM kits focus on the details of a particular setting and may not let other character settings really shine. The EotE GM kit module focuses on a deal with a Hutt...the F&D focuses on finding a location beneficial to Jedi. As I said, that doesn't mean that a Rebellion Spy wouldn't have anything to do in the EotE module...or that a slicer would be sitting on their hands in the F&D module...it just wouldn't give them as much of an opportunity to really show what they can do.
The kits DO contain information expanding on ideas found in the three core books. As was stated above, the AoR module is going to help you run large-scale combats and battles. The EotE module has information on how to 'build' a Nemesis for your party, and really make the guy memorable. The F&D module has information on constructing lightsabers, and tips on how to run 'Knight Level' (read: high-powered Jedi) modules and adventures.
Bottom line: Should you get all of the GM kits? Probably not right away. If your group is happy running AoR, then grab the AoR kit and have fun. Will you want them all? At some point, yes. Even if you don't play all of the settings (EotE, AoR, F&D), there's useful information in each of them.
I'd go for the Age of Rebellion GM kit because the squad rules in the kit will likely be the most useful and fun.
F&D would be my last choice. The lightsaber hilt construction rules are nice but they are a minor addition to gear rules that already exist while the squad rules from AoR add a whole new rules option. Also, the F&D GM kit advice on managing groups with Knight Level characters offers good but mostly obvious advice.
Another consideration is that each GM kit comes with an adventure - so if your group (or GM) really wants to run from a planned adventure (and isn't using one of the already published adventure books already) then there will be value in the GM kit line which more closely matches the campaign/group focus.
If you're only getting one, the art from the Edge of the Empire one is my most favorite. The adventure in that one is a lot of fun, especially for turning the typical murderhobo party on its ear.