An old book that still works today

@eladar said
@mchill

One plus for this approach is that although this is a classical approach the defenses are not as popular these days. That means it is quite likely your opponent will not the positions as well as you.

That's true, in addition, I played through dozens of games of Anatoly Karpov at the peak of his power and was amazed at how he used the Caro Kann and occasionally the Slav to totally demolish the strongest grandmasters of the day, even though he had the black pieces. These 2 defences may look tame, but they're brutal in the hands of a skilled player.