Your quality will look the same upon rendering as long as your quality settings are Best/Full.
The diffence is this. Your monitor is only can display so many pixels—Looks like you’re around 1280x, maybe 1600x. If you choose “fit”, the composition will scale to fit inside the composition window, you’ll see the entire thing. In your case to make the 1280 fit inside the window, it scaled it down to 87.9%, but caused some distortion.
At a 100%, if your comp window is say only 900 pixels across-the 300 pixels on either side will be cut off in the preview, but your quality will be at it’s max. The infomation is still there, you’re just not seeing it.
You could play around with a graphic and test this out…set to fit and make the graphic stretch from all the way across the screen. Now change to 100% and you’ll see that the sides of it are cut off.
Glad I could help.
Johnny Cuevas, Editor
http://www.ckandco.net