Quality with the screenshot tool isn't good

Shutter

My suggestion would be to use a screen capture tool such as Shutter.

sudo apt-get install shutter

If you look in the preferences - you can define what the compression ratio is together with the graphical format.

If you don't want to install yet another program give Gimp a try. File->Acquire->Screen Shot...

The images are fine, but they look blurry because the default Gnome Image viewer is set to "Best Fit" instead of "Normal view", which resizes images slightly, making them appear blurry. Unfortunately, there seems to be no preference or setting that allows changing this. Instead just install another image viewing app, and make it the default:
sudo aptitude install gthumb
It can be customized to view images 1:1 by going Edit -> Preferences -> Viewer -> Set to actual size. Then go View -> unselect "Thumbnail pane" (with this on, it seems to interfere with 1:1 viewing). Test it, then if so make it the default app by going ubuntu "System Settings" (top right corner of your desktop) -> System info -> Default applications -> Photos -> gThumb.