I just picked up a GM screen from my local game store. It says "Edge of the Empire" on it and I was wondering, do all the games have their own screen with different unique information or are they all the same just with different missions.

The screens themselves vary only slightly, with the weapon tables differing depending on the book. They each have their own adventure, but the bit in the back of the adventure booklet varies from each. Edge of the Empire covers making nemeses, Age of Rebellion provides rules for squads and squadrons, which are pretty nifty, and Force and Destiny offers advice on Knight level games, and preliminary lightsaber hilt crafting rules (which are kind of obsolete with Endless Vigil, but could still be useful).

The squad/squadron rules are probably the most useful, but the adventures are worth it for me.

Force and Destiny offers advice on Knight level games, and preliminary lightsaber hilt crafting rules (which are kind of obsolete with Endless Vigil, but could still be useful).

The rules in EV are not meant as a replacement to the ones in the GM Screen. They provide 2 ways to go about the same thing. The EV ones really shine if you have dropped 3+ levels into Mechanics and have a 3+ Int. If your character is less mechanically inclined, then the GM screen ones work much better