Which is better the french defense or the caro-kann?

Both French and Caro Kann have their owns tastes. It depend on your style of play that you decide your repertoire. French is very complex and tend to be tactical game, while the Caro Kann is solid and positional game. Caro Kann was used by M. Botvinnik and later A. Karpov in their World Champion Matches to defend against tactical super masters (M. Tal and later G. Kasparov)