PNG vs JPG: which should you use?
Use PNG for screenshots, charts and text. Use JPG for photos.
When PNG is better
PNG is lossless, so nothing is thrown away. Edges stay sharp, and it supports transparency. The cost is size: a photo saved as PNG can be many times larger than a JPG.
When JPG is better
JPG drops detail your eye barely notices, which makes photos far smaller. On text and thin lines, though, you may see blurry halos around the edges.
Saving again and again
Each time a JPG is re-saved, a little more quality goes. Keep your original if you plan to edit it.