Are we talking best leagues in the world or just Europe?
In either case, what is there to judge? Competitiveness? Unpredictability? Success in Continental tournaments? Quality in their players?
I would say that normally, Bundesliga, Campeonato Brasileiro, and Argentine Primera Division are quite unpredictable. Its true, that Bayern Munich usually is within the 4 top of the league, but there are always 7-8 teams aiming to fight for the title. In Brazil, you have always big teams, big names and Champions rarely repeat. In Argentina its even worse, the big teams are struggling a lot, and teams like Lanus, Banfield, Estudiantes and Argentinos Jrs claimed recently the title.
Ligue 1? Just recently has it changed. Nobody remembers the 7 titles in a row from O. Lyonnais? In Europe they always struggle. I believe last years Lyon was their best finish in CL in the past 5-6 years.
Dutch League? It used to be always between Ajax, PSV and Feyenoord. Now, some other teams have joined the battle, Alkmaar, Utrecht, etc...Still quite predictable.
As for the Premier League. True, its always between 2-3 teams, but the games are great in general. And anyone can win. The fight for the European spots are more interesting than the one for the title.
La Liga? Arguably has the best players. Still the league is always between RM and Barcelona. The rest, fights for different objectives throughout the season. Valencia, Villarreal, Sevilla, ATM had great starts, but com on, who are they kidding, as soon as they face the "Batman &Robin" they are finished.... like always.