There’s counters to it, including a Gambit, and well prepared opponents will put you right back into a Vienna type game.
What is the BEST OPENING AS BLACK AGAINST 1.E4?

There’s counters to it, including a Gambit, and well prepared opponents will put you right back into a Vienna type game.

If your willing to book up either a Sicilian you like or an aggressive set of 1.e5 openings would seem to suit your style. If you're wanting something more offbeat maybe Pirc, modern, or Alekhine.

There is no best opening against 1.e4.
Since you already play the Caro kann, you could give the Scandinavian a try. You will have the same pawn structures in general, a semi open board, and the Bishops do a lot of work till they are traded off.

c5 is usually an important move as black against 1 d4 and 1 e4 openings so you may as well get it out of the way with the sicilian. Playing the sicilian requires extensive preparation however. The best response to 1 e4 really is the one that results in positions that you like to play, so experiment. I play e4 and d4 as white, and play c6 (caro) vs 1 e4. After a few years of playing the caro I'd say i have most of the lines down well. It can be boring for sure but that's kind of the point, have no weaknesses and a good pawn structure and bore your opponent into making a mistake or trade down to a winning endgame. There are alot of aggressive responses from white to deal with in the caro however.
personally I would do the sicillian