You have to select the right filetype for the type of image you're compressing. If you're compressing a photo, or something with lots and lots of shades and colours, use jpeg. If you're compressing something that has been "drawn" then png is the way to go. When I say "drawn," like.. Runescape has been drawn using shapes and colours, so png offers the best compression & quality. In almost all cases, png is better than gif.