I have found that on it’s own no algorithm does really shine when it comes to heavily degraded video.
The Artemis low quality one is supposed to be suited for this but it turns out to over sharpen high contrast areas and leaves low contrast areas too smooth. It’s also not as resilient to artifacts as you might think and often turns shadows into additional edges giving quite an unnatural dream like look.
While I was able to get somewhat better results with the proteus algorithm where you can tune it so edges look alright it suffers from a similar problem when it comes to texture.
That out of the way I am able to get very decent result with a two pass process.
First restore the video using gaia-hq or gaia-cg without scaling. (100% deblock) then upscale using artemis-lq.
Gaia is quite resilient to all kinds of noise, grain and compression artifacts and it really does a good job with enhancing degraded textures.
The choice between hq and cg is a matter of preference. Gaia hq is slower but dreams up more details while cg is faster has even better resilience to artifacts but it doesn’t enhance the textures as much.
The output of gaia is then fed back into VEAI using the artemis-lq algorithm with scaling. This works great because artemis-lq will enhance edge sharpness when scaling and the lq algorithm also does a great job discarding the additional artifacts gaia introduces while preserving the texture gaia “dreamt up”
That’s almost a best of both worlds for me.