I needed to store a large quantities of images so took the following measurements:
|ppm||0.648540||1769488||Browser does not support PPM|
|tiff||1.011216||1769600||Browser does not support TIFF|
Gif is the clear loser - it takes a long time to process but still looks terrible.
For space use jpeg, speed ppm.
Google’s new WebP format looks promising.