Q:
Full Screen vs Windowed FullScreen
A:
Full screen locks you into the screen until you ALT-TAB out, while Windowed Full Screen allows you mouse to freely move to a non-primary screen (so you can perform OS desktop or other program actions while the GW2 screen remains active on your other monitor.
I see very little FPS difference (Windowed is slightly better), but this highly depends on your video hardware, video settings (both in game and Windows) and your drivers.
Note that all of this is based on running via Windows OS (I have no idea about the MAC client, but I would think it works similarly).
Fate is just the weight of circumstances
That’s the way that lady luck dances
so, better is to run Full screen than Windowed Fullscreen?
Not for me, but you mileage may vary. Are you actually running multiple screens? If not, you might want to try both (you can change while in game) and check your FPS and performance in general. Without a 2nd display, I doubt you can tell the difference.
Fate is just the weight of circumstances
That’s the way that lady luck dances
Full screen should be faster since its not also rendering all your desktop stuff at the same time (reason why atl-tab is so much faster and smoother in window mode). Also amd crossfire does not work in window mode
What Nick said. Full screen gives better FPS since the desktop isn’t rendered.
As for the Mac client, since Mavericks, the only thing that is rendered is what is seen on the screen, as opposed to also rendering what is hidden behind other windows. So in theory, the difference in FPS between windowed and full screen might be less than it is on PC.