This is an interesting topic. I hope it can remain civil.
Lewis > Alonso (based on 2007, but not by much, but also considering this was Lewis's rookie season)
Lewis > Button
Lewis > Rosberg
Lewis > Bottas
Alonso > Kimi
Alonso > Massa
Alonso > Button
Bottas > Massa
Vettel > Kimi
Vettel < Riccardo (not by much, and perhaps to some degree also due to the car not to his liking)
Vettel < Leclerc
Verstappen > Riccardo (not by much to be fair, but enough in all areas)
Verstappen > Sainz
Considering this, I think Lewis, Alonso and Verstappen are top tier. The big question would be, how does Lewis fair against Verstappen and vice-versa? I think it'd be close, because both drivers show the ability to perform extraordinary out of difficult cars. I personally still rate Hamilton higher on the basis that he has faced fiercer opposition in multiple champions to single champions, where as much of Verstappen's image as a killer of team-mates is against drivers I don't rate that highly (Gasly/Albon). Therefore, I think Verstappen's sheer talent might just be slightly exaggerated, just as some might think Hamilton is not that great using Bottas as a yard stick.
Alonso is a tricky one, because I think Hamilton is better, but Alonso has shown extraordinary performance against pretty much everyone since. I therefore think all 3 of them are within the same "tier".
Vettel is interesting too, because he underdelievered against Riccardo, although one must say under difficult circumstances too (a car not to his liking). Riccardo, I feel ran Verstappen close, even if lacking that raw speed Verstappen has. On this basis, I'd conclude Verstappen > Riccardo > Vettel.
Leclerc I think is one of the big talents of the future. He utterly dominated F2 and I think 2019 (not 2020) showed his skill vs Vettel when he went on to take pole after pole but also withstood the pressure of being hunted by Hamilton in multiple races. He is also continuing to impress in 2020 in dragging a car well into the points in what easily and evidently a very difficult car. Having said that, Vettel and Leclerc were very close in regards to their qualifying match-up. According to my calculation, the difference was
2019 Leclerc : 11 vs Vettel : 9 (55% / 45%)
--- Total avg diff : -0.070
--- Total avg per km : -0.005
Despite this (or because of), I'm not sure I've seen enough to put him into "tier 1". Next year will be telling when facing off with Sainz - someone who has gone against Verstappen and not done such a bad job. Under the assumption that Leclerc is tier 1 material, I would expect him to be better than Sainz and with a comfort margin.
Anyway, putting all the above in context; in my opinion:
Kimi, Massa are below tier 3.
Strangely, I had Rosberg in Tier 2, but have decided to put him into tier 1. Maybe 1.5 would be more to the point. One reason for this is because Rosberg was fricking fast in qualifying. He outqualified Lewis in 2014 and the margins were always very close. I also think Rosberg could also challenge Hamilton during the race. He certainly had more grit as a racer than Bottas does and I think this is Bottas's biggest shortcoming and also something that puts Hamiltons performance into perspective; He is relentless and as such, I can only pull my hat for him for that 2016 championship. Contrary to others, I also don't think those performances from 2010 to 2012 were a fluke against Schumacher. Rosberg was that good. From that group within tier 1 probably the slowest, but I genuinely think he'd present trouble for anyone driving against him. Getting under someones skin (aka Hamilton in 2014-2016) is also part of what makes him that good and is a skill. To be fair, the fact that the Mercedes was so dominant in those years might have helped Rosberg hide his subpar performances. I think Bottas faces far higher scrutiny because he is racing against Hamilton in an era where the margins between teams have been smaller. Overall, I think Rosberg > Bottas at this point. Perhaps not in qualifying where Bottas is really close, but overall, I think Rosberg was the fiercer competitor and this puts him above for me.
One last thing; the most impressive thing about Hamilton, Verstappen and Alonso is that they perform extraordinarily in difficult circumstances. This is what influences my personal order of these driver the most and in this area, all of them excel.
Disclaimer: This list of mine isn't definite btw and subject to change when more data is available.