FSR implemented within the game has the advantage (aside from being hardware agnostic) of the upscaling being applied to the actual 3D portion of the rendering only, exclusing menus, fonts and stuff, which will remain sharp. Using RSR is a general approach which will also process text, menus and such. It's pretty cool for Radeon owners, of course, as they do not need to use any additional software and just tick a box in the control panel. And then there is FSR 2.0, which will not be implemented on the driver level, as it requires specific motion information from the engine.
Nvidia offers a similar technique, but their solution, NIS, is quite inferior. FSR and RSR can work pretty great in 1080p resolution, even when upscaling from 720p - it only makes the image feel a little "plasticy", but the performance uplift is worth it. The higher the resolution, the better, of course. NIS looks terrible in comparison, at least in 1080p where the source resolution is quite low, but AMD's solution does wonders in comparison. I hope Nvidia comes up with some "deep learning" alternative soon.
The Lossless Scaling software seems interesting for non-Radeon owners, so I might buy it later today and report my findings.