.jpg is a better option for images/photos with lots of colors. Its compression is a bit lossy, but the quality is still good for web viewing, and the good thing about it is that it has small file sizes which is ideal for the web.

Use .gif for black and white images or images with few and solid colors, since a .gif file will result in a smaller file size in these cases.

.png is useful for transparent rendering, although the file size is a bit bigger than usual, which is why only a few websites use this option.