The answer depends on your individual needs. When it comes to choosing between JPG and PNG, the
first thing you should decide is what you're using your images for and for how long you'll be
If you're creating images for web use (which usually means putting them on the
Internet or sending by email) then you should use the JPG format, since it's smaller and quicker
to download than the other formats.
If you're creating images to be printed in magazines or
newspapers, or if you need transparency information (for example when putting an image over
text), then choose PNG. But you do not have to worry as the online png to jpg converters convert
the images in no time.