In this case it should probably be a JPEG? (Unless it has a transparent background and the site responds to the user's dark-mode setting? :) Also, this image looks like it almost certainly was a JPEG, at some point!)
The color palette is pretty limited, so using something that can have a specific/limited palette (say 48-64 color in this case) is probably going to have a better result than jpeg. Also, optimizing for display size would take it further still. Alpha transparency support is also a bonus for png over jpeg.
