yeah actually.... jpg is designed for photos.
If your image is not a photo it will probably look horrible in jpg.
Only use jpg for high-res photo-like images that have no alpha and are to be loaded on runtime. For anything else go with PNG.
I'm using jpg for photo background images
Oh and you can control the compression error in JPG. Of course, as error is reduced, size approaches (and surpasses) that of a PNG.