This file has a .png extension, but it's actually a 1011x1280 JPG:
(154,559 bytes)
http://www.furaffinity.net/user/essien/
http://www.furaffinity.net/view/13004001/
http://d.facdn.net/art/essien/1395291460.essien_6_copy.png

This version really is a PNG, but it's only 789x1000:
(1,395,042 bytes)
http://www.furaffinity.net/user/wanny/
http://www.furaffinity.net/view/12980298/
http://d.facdn.net/art/wanny/1395023822.wanny_essiencommish.png

e621 has a policy of keeping the best version of a pic.
In cases like this, it can be hard to decide which version that is.

So... Instead of flipping a coin and picking one, you suggest seeing two of everything? I'm not a fan of drinking, I'm afraid.

I usually just keep the older one or the PNG, but I'd rather we didn't keep both

I've seen this problem before, and I'm inclined to keep the one that hasn't been compressed, even if it is smaller. The difference in size is relatively small compared to the compression. The automatic resize is why I tend to be wary of FA or tumblr uploads.

I can't access FA to compare the two images, but if there's no noticeable change in quality of the higher resolution JPEG I'd probably think it might be better to go with that. Or maybe ask the artist for the highest res PNG.

The JPG has compression artifacts. So I think the other one should be kept, even though the resolution is smaller.

Quality > size, every time, unless the image is for ants.

I'd rather just see the better one, as my computer is not a potato :o