The best? The best is Spain. Not only is the best teams there better than those in the PL, Seria A P, Bundesliga etc., but the sub top (Sevilla, Villarreal etc) are very good too. Villarreal narrowly lost 0-1 at Camp Nou last season while drawing 2-2 at their own ground. Same with Sevilla against "the big three". They may not get the same amount of points against other opponents hence why the finish below Barcelona, Atletico and Real Madrid. But make no mistake, they are very good teams. Their success in Europa just accentuates that.
Hell, even Deportivo took points at Camp Nou, while Celta beat Barca 4-1 at home not too long ago. 4-1. Celta are in that sub top, but Deportivo are nothing special. Real Sociedad constantly beat or draw Barca at home. There are plenty of those results, also involving Real and Atletico. The latter lost points against Alavés and Leganés in this season. Yes, the CL finalists drew against two newly promoted teams. Top top league with plenty of competition despite the occasional battering by Barca and Real. You could be sure they'd do that if they played in other leagues too. That's just a consequence of their ridiculous talent. When you've got Messi, Neymar and Suárez and they all feel it, there's nothing you can do.
And before someone mentions "but it's only been a two horse race, maybe three now". Look at the PL winners from the last 10 years or so. How much difference is there? Not a thing - bar Leicester of course. Leicester winning has more to do with the incompetence of the top teams last season. They wouldn't even have finished top 3 in Spain despite having played some good football.