Meatsack summary using quotes and [paraphrased quotes]:

[…] FSR 4 image quality generally sits somewhere between DLSS 3 and DLSS 4. […] I think in most cases FSR 4 will meet your requirements for image quality using either the Quality or even Balanced modes and you’ll have a pleasant experience using it.

[…] In my opinion I’d be happy playing games with FSR 4 at 1440p, and I also would be happy paying a small premium to access DLSS 4. Anything more than that and you’d have trouble convincing me to spend more on GeForce, unless the GeForce GPU had many other compelling features.

[because titles supporting pre-3.1 FSR can’t be easily upgraded to FSR 4, the difference in titles which support “acceptable” upscaling quality via DLSS 2+ vs FSR 4] leaves real world game support heavily in Nvidia’s favor. I’m hopeful that at some point in the future the gap in game support closes, along with the remaining gap in image quality, but it’s going to take a lot of work from AMD. […] Until that happens, AMD is in a bit of an “early adopter phase” with FSR 4. Yes, the upscaling gap has closed to some degree, but it may not be closed in the games that you want to play, so you’ll need to factor that into your value calculations when tossing up between GeForce and Radeon, at least for the next 6-12 months.

[Hardware Unboxed will test FSR 4 at 4K and 1080p in the future but will take a short break before doing so, because] these videos take an enormous amount of time [and they’ve done so much testing on upscaling recently.]

edit: typo