#1 Barcelona

A lot had been said about whether Barcelona were on the decline, when Ernesto Valverde was appointed as their new manager and the Catalans have proved everybody wrong by putting in one of the most impressive campaigns in recent history, so far.
Barcelona hasn't lost a single match in their domestic league and have refused to do so in the Champions League as well. Their only loss of the season was in the first leg of their Copa del Rey quarter-final with local rivals Espanyol, a minor hiccup that they corrected in the second leg.
Ironically, the loss came when Barcelona rested almost all of their first-team players, meaning that their full-strength line-up is still unbeaten this season.
While Lionel Messi is back to his brilliant best, it's the team's defensive record that should really strike fear into their opponents' eyes. Barcelona have only conceded 10 goals this season, meaning that they have obviously fixed what many people thought was their Achilles' heel.
It will take a lot to beat Valverde's team this season, particularly in Europe where it will have to be done over the course of two legs. The Blaugrana look absolutely unstoppable at the moment and rightfully deserve their spot as Europe's most dominant team.