There are many fine domestic leagues in Europe but only a handful of them are truly excellent. Spain, Italy and England's domestic football [soccer] leagues are all ahead of the pack, because of money, home grown talent, sustain and excellent skill sets. But as far as the top league in Europe, I would have to put Spain ahead of them all.
The presume I have the Spainish La Liga as the top domestic league in Europe is because of the high capability and quantity of soccer they show week after week. For example, you have Lionel Messi the top player in the world playing for Barcelona, Iker Casillas the top goalkeeper in football, Thierry Henry, Samuel Eto'o, Raul, David Villa, I could go on but you get the idea. And also besides Real Madrid, most of the Spanish teams have a considerable estimate of "home grown" talent from Spain playing considerable roles on their teams, or as substitutes, which is very tough to do while competitive at such a high level.
Look at the English Premier League, it is very tough to find more then 3-4 English players on any of the top 4 teams. On the top 4 Italian teams in Serie A at least 6-7 starters are of Italian descent, which is similar to Spain's top 4 teams. This is an additional one presume why I must put Spain's La Liga ahead of England. an additional one key as I said is not only the capability but the quantity, there are about 7 dissimilar teams in Spain that have a chance to win the League Title, unlike the leagues in England and Italy were the same top 3 or 4 clubs consistently win. Five dissimilar teams have won it in the last 15 years, and a team like Deportivo de La Coruña, has been 3rd three times, and 2nd four times, but on top of that the other six teams that are normally competitive every year for the title, are Atletico Madrid, Real Madrid, Barcelona, Valencia, Villarreal and Seville. The teams in bold have all won La Liga title in the past 15 years.
The Best Domestic League in European Football (Soccer)