It is annoying how so many commentators continue to repeat erroneous views that Ederson is the best goalkeeper in the league, when Alisson is better at him in virtually every single metric of goalkeeping except maybe short range passing. Ederson is an inferior goalkeeper to Alisson and that is why he is Alisson's understudy for Brazil.
Alisson is better in long passing (he plays more successful long passes) and their overall pass percentages in PL is Ederson - 82% & Alisson - 80%, the marginal difference could be due to the higher amount of longer passes that Alisson attempts on average. You could give short passing to Ederson, the weight on those passes from Ederson is better.
But beyond that, Alisson makes more number of saves, saves more percentage of shots, has better positioning and is simply the better shot-stopper. Both come off their line and command their area equally well.
Considering all that, Alisson is indeed the better keeper, but the failure of media to acknowledge that is kind of expected. Alisson did make a couple of mistakes early in the season (although they were just consolations to opposition from our view, none of them costs us and he saved us an entire CL campaign plus plenty of points in the League across the season). Ederson has been here longer, they are yet to warm up to Alisson in that manner. Ask Roma fans, Serie-A fans and Italian media and they'll straight away say that Alisson is better. That's how it goes. A couple more Golden Gloves in the next 2 years, and it will surely tip it in Alisson's favour with the English media.