The SCART socket is primarily there for people whose TV doesn't have HDMI sockets. But it can also be used to connect to a VCR/DVD or to send the picture to another TV in a different room.
You can use the HDMI lead for every channel.
I'm not really sure what you mean about the background being blurred. It's normal for some parts of a picture to be out of focus, and it's often the background - that's how lenses work, including the ones in your eyes (see the examples
here). But try adjusting the picture settings on your TV, and you may be able to make it more to your taste.