I went AMD these last two generations with a 6950XT and 7900XTX. No issues with the cards or the drivers, and the software suite is much better than Nvidia's. Obviously the RT performance is not on par with NV, but on the 7900XTX it's good enough for games that have some RT effects, but falls off considerably as you get closer to full RT path tracing like that Cyberpunk tech demo. Hardware Unboxed
revisted the 7900XTX vs the 4090 and you can see that RT is competitive until, for some games, it just isn't and falls behind completely.
I think the biggest downside with going AMD is that they will always be behind on software features. DLSS will always be better than FSR, NV frame gen will be better than AMD frame gen, etc. Even Intel's native XESS might have already passed FSR in terms of quality. At best, I think AMD tries to make these features good enough in the hopes that they become the de-facto standard (like FreeSync). This is why FSR isn't better on AMD hardware than on NV/Intel. (While DLSS is exclusive to NV and XESS has two modes, with the better DP4A mode requiring Intel hardware). At worst, AMD uses these features to tick off marketing boxes and they will never be fully competitive.
By defination there will always be input lag with frame generation, but it can be minimized. It works by processing a real frame 1, then another real frame 2, and finally generating frame 1.5. The frames are shown in order 1, 1.5, 2, etc... but always slightly delayed since future frames are needed before the generated frames can be created. This is why frame generation works (or feels) better on cards with better base performance. If the card can natively do 80 or 100FPS than using frame-gen to push that to 120+ won't feel like there is too much input lag (or perhaps none at all). Conversely, if a card can only do 30-40FPS for a given game/settings then using frame gen will boost FPS but will also give it more input lag.