Which league is the best in Europe? While it is certainly possible to group leagues into better and less good leagues, it is hard to find a universally recognised scale.
The highly recommended blog and football statistics site Goalimpact has published the average Goalimpact of each of the Top 5 leagues since the 90s (link).
While I am quite enthusiatic about his methodology, the results were a bit disturbing. The Bundesliga better than the Primera Division for the last 20 years? Certainly, Goalimpact also takes National team performances into account and not just clubs, but anyway, this does not look right.
I am throwing my own calculations into the ring, the average Elo value of each league:
A few things need to be taken into account:
The leagues have different sizes, so taking the average slightly favors small leagues like the Bundesliga.
English teams were not allowed to compete in European Cups between 1985 and 1990, the English Elo values of that Era are uncertain to a degree.
Elo values from the 60s or earlier are not waterproof either due to arbitrary start values.