I would put Barcelona first to win this season. One of the simple reasons for this is that Barcelona has a balanced team and their coach is also very skilled, especially in big matches we see great planning and strategies from Hansi Flick to defeat the opposition. My second choice would be Real Madrid, I don't think it's unfair to put Real Madrid second. They have just changed their coach and Xabi Alonso is not used to Real Madrid yet, he is not even proven with big teams. So for now I can't put Real Madrid first in the list of favorites to win this season. On the other hand, Atletico Madrid's team is not in a good shape at all, I don't think they are a strong enough team to fight for the La Liga title at the moment.
Hansi Flick's Barcelona can really win a lot this year if they commit themselves and manage all the talents they have at their disposal. They can do really, really well. The players are available and there are many of them, you just need to know how to choose well.