Ultimately, the toughness of each league can be subjective and may depend on factors such as team strength, playing style, and individual matchups. Its English Premier League. It is hands down the toughest league to win. The top 6 sides are always competing hard and investing in talent.
If we look at the figures for the last few seasons, the Premier League earns far more than any other. Compared to LaLiga, the English competition's revenue from television rights is almost double over 4 billion versus just over 2. billion. This explains much of their spending power.