In general, because JPEG files are compressed, they are the better choice, and help improve your site's loading time. JPEG files have enough image quality for most sites on the web.
If you have special image requirements, and you want to upload high-quality images or images with a transparent background, PNG is the best format. PNG file formats should only be used when necessary, because a large number of high-quality images can increase site loading time.
GIF files are recommended only for animated-gifs.