Been wondering this for a while since to me it seems very inconsistent in terms of which is prioritized. Obviously in situations where the resolution is equal the PNG version should be uploaded, but I've seen cases where a much higher resolution JPEG version was deleted in favor of a lower resolution PNG, and vice-versa where a PNG was replaced with a higher reslution JPEG. Or is there maybe a third part of the equation that I'm missing? Either way I'd appreciated some clearer guidelines over what I should be aiming for.

A lower resolution PNG is usually preferred over a higher resolution JPG. There may be some exceptions, like if the JPG is massively larger in size or if the PNG is too low resolution that it loses the fine details or readable text.

I really wish people would just start uploading their art to better places because it usually comes down to picking from Fur Affinity (PNG squashed to half its size) or Twitter (JPG with 85 quality).

faucet said:
I really wish people would just start uploading their art to better places because it usually comes down to picking from Fur Affinity (PNG squashed to half its size) or Twitter (JPG with 85 quality).

True, as far as specific examples I know Inno-Sjoa tends to upload their stuff on Twitter as around 3900x2500 JPEGs and on FA as (still pretty damn big but much smaller) 2400x1500 PNGs, and I had the former replaced with the latter. WOndering if there's a threshold for the size difference to matter.

There is generally no size difference threshold. What matters is a subjective comparison of visual clarity ("How clear are the outlines?") and compression artifacts ("How crusty of a JPEG is this?"). The higher-resolution image usually has higher line clarity, but varying levels of visual artifacts.

Standard practice is to open both versions in new tabs, zoom in to the same or approximately the same level of detail on the same spot, and make a judgment call based on those two metrics. In an ideal world, we would all be using sites that support high-resolution PNGs and rely on resolution as the sole arbiter of quality, but there is sadly some level of subjectivity due to Twitter and Fur Affinity having their own, very different types of restrictions on image quality.