I have the complete edition of TW3 and the Become As Gods edition of Nier.
Looks like I'm going to start with TW3. I kind of wanted to start there anyway to get prepared for Cyberpunk.
Difficult choice between Nier Automata and RDR2. Both are excellent games. I couldn't vote for Witcher 3 as I thought the controls were quite frankly arse.
Although I appreciated the scope, detail and graphics of RDR2, it was a game I had zero interest going back and I can't exactly pinpoint why? It's just not that fun I suppose? But it should be? It's hard to explain.
Neir is really overrated. Simplistic combat, bland environments and boring story. It was short enough and just good enough that I completed it, but it was just mediocre.
They're all very different. How much tedium do you want in the game? From least to most:
Nier
Witcher 3
RDR2
I'd personally say park Witcher 3 until the next gen patch which is free. It deserves that patch. In the meantime play RDR2 - we don't know if it's getting a patch but we know online will still be going so it will let you drop it or stick with it fairly quickly.
Go for Nier first as it can be finished in a reasonable time compared to the other 2. All 3 are great games but RDR 2 and Witcher 3 can easily eat 50+ hours.
I would say The Witcher 3, because it's worth playing, arguably, the best video game (or at least RPG) ever made, but you might want to play it in 2021, when the final patch drops. Second choice would be NieR: Automata.