One of my top recommendations for Black against 1.e4 is the Caro-Kann Defence. Not only is it solid, it also fosters good positional understanding by virtue of the nice variety of pawn structures and concepts it contains.
It’s no accident that the Caro-Kann has been played by many of the greatest positional players in history; Aaron Nimzowitsch, Jose Raul Capablanca, Mikhail Botvinnik, Vassily Smyslov, Tigran Petrosian and Anatoly Karpov. All these players would have been attracted by its inherent qualities and it can also help foster them.
Here’s a crushing win with the Caro-Kann by Anatoly Karpov over Nigel Short, Karpov effectively reducing his opponent to utter helplessness:
How should someone learn the Caro-Kann? I offer what I think is a good approach at my Tiger Chess site as explained in the following video: