There is no one definitive answer to this question. It depends on a number of factors, including the format of the image, the size of the image, and what you plan to do with the image.
JPEG is a lossy format, meaning that some of the detail in the image is lost when it is compressed. However, it is also a very popular format for storing images, because it is typically a smaller file size than other lossless formats like TIFF.
PNG is a lossless format, so no detail is lost when it is compressed. PNG files are typically larger than JPEG files, but they can be useful for things like images with transparency or text.
GIF is also a lossless format, but it is limited to 256 colors. It is often used for small images, like website icons.
There are many other image formats, but these are the most common.