Now, as for quality of screenshot, there are a couple of things to note:
First, make sure you are saving in PNG format for screenshots (the only exception to this would be if you are capturing mostly photographs and want small file sizes).
PNG is a LOSSLESS format, which means that the image will be an EXACT copy of what you see on the screen, with no blurriness or loss of quality.
HOWEVER, what does confuse people sometimes is that when a large image (say of your whole desktop) is DISPLAYED on the screen and has to be reduced in size, there are different ways to display the smaller version of the screenshot which may look more or less blurry on the screen.
It's important to realize this is only effecting the quality of the DISPLAY of the image at that size, not the inherent quality of the stored image.
You can see that by clicking on the upper right of the Screenshot Captor main window and going to 100% zoom, which will show you the original image quality, rather than the image reduced in size for display.