Deciding who is the best driver of all time is impossible because cars have evolved massively since 1950; personally I would suggest Fangio is the best driver of all time because back then it was more about driving ability as there was nothing more than a big engine, 3 pedals, gearshift and a chassis that would likely kill you if you crashed.
That aside, is Lewis the best of his generation, maybe, I would say it's between him and Alonso, Vettel needs to prove himself without a class leading car to be elevated to the level or Alonso and Hamilton. I don't think that anyone can deny Hamilton's talent, you don't become 2xWDC without having immense talent.
Good point there in that it is not possible to declare the GOAT due to eras. What we can look at is the generation and the drivers delta to his generation. He would have to be indisputably the best of his generation, or at least arguably so, like Senna v Prost. I think Alonso and Lewis are the best of this generation. However his claim to be indisputably better than Alonso grows with the evidence and ofcourse can only be truly assessed at the end of both careers, with Alonso in the last chance saloon and Lewis in the top dog role for now.
My point was that, the metric Alonso is most feted by - completeness and effectiveness is now demonstrably owned by Lewis. Its just that the pundits who declare Alonso best because of these traits have now gone silent when its time to make another comparison based on the latest facts. The TPs believe Lewis in a top car is better than Alonso by more than Seb was in a top car, so Sebs claim appears to have faded. Alonsos claim by dragging a lesser car above its place was not seen as ultimately better than Seb in the best car last year.
And we know that Lewis is faster in quali and in the race - from when they were teammates and since then Lewis is the indisuted 'most complete' of the bunch. 2 WDCs in 2 teams, dragging a car up the grid in 2009, dominant in a dominant car and then the all important metric of quality teammate. Alonso has not had this and choked the one time he did have it. Whereas Lewis has despatched alonso, Button and Nico in fine style. Lapping one in identical cars in normal conditions, beating another on pole from the back, and ofcourse beating the other as a rookie.
just a shame the stats experts and the brundles etc have not yet seen fit to compare the 2 with the new data we have such as most wins in a certain number of races, qualis, fastest laps etc. And even picking the right teams and producing results. Alonsos stock has been reduced by his failure at Ferrari, either the teams fault or his, but ultimately his responsibility and his reputation. Any unbiased pundit asked to compare the 2 today would have to conclude there is no evidence at all anymore that Alonso is the best.
And the TPs say lewis is by a bigger margin than previous best of the years