is the French defense really the most aggressive?

I need to find a good opening for black

No.  The French Defense is generally not considered one of the more aggressive responses to e4.

The Sicialian Defense is among the more aggressive. 

Of course, it all depends on how you play them.  Two moves isn't enough to tell.

The French Defense is an extremely ambitious opening strategically... it intends to take control of the game and dictate the play by launching an immediate (move 2) attack on White's e4 square.

'I have never in my life played the French Defence, which is the dullest of all openings.' - Steinitz

Robert James Fischer vs Mikhail Tal (1960) French Drawings (chessgames.com)

Traditionally, the French was the most aggressive response. Now that things like the Advance with a3, the Tarrasch and the Exchange have become weapons to nullify the French, that's in doubt. The Sicilian is less overtly aggressive than the French .... in reality it's white that tends to adopt an aggressive approach to the Sicilian. That's due to the pawn formation, which will increasingly favour black as the game moves towards the late middle game. However, the French depends more on memorisation of exact lines, whereas the Sicilian depends less on that. The Sicilian scores well at a high level but the French is innately more aggressive and is probably the best response for you.

Yeah well, Steinitz was wrong. It isn't as if he had the reputation of, say, Louis Paulsen or, later, Tarrasch and others, as a brilliant commentator and innovator.

'The Defence is anti-positional and weakens the king's side' - Fischer
'at best a second-rate opening' - Carlsen

'After Pawn to King 4, White's game is in its last throws' - Reti (?)

EDIT: Breyer! It was Gyula Breyer, not Reti.

You don't need a better opening for Black, what you need is to study opening concepts and learn more opening theory as you play. Against 1.e4 playing 1...e5 is much better overall. The French defense requires a high level of strategy that you won't really take advantage of yet.

When you get to 2000 elo maybe you can take better advantage of the French defense, although in reality it requires a strategic level close to 2500 to really take advantage of the virtues of the French defense.

Keep playing 1...e5 and study games analyzed by good authors, study opening theory and choose a particular line for each variation. If you accompany all that of studying tactical issues and calculus, also studying concepts of endings, then you will improve a lot without even realizing it.
Also study your own games, you will find your common mistakes and the most frequent mistakes of your opponents.

If at some point you want to get out of your comfort zone, you just have to change some variations and opening lines, you don't necessarily have to stop playing 1...e5.

I mostly play French Defense - I wouldn't call it "aggressive", but it's a safe/easy opening for average players and has a few tricks that blitz players sometimes fall for. The "advanced" variation is the most fun (for black) - it's all about applying pressure to the d4 pawn. A few mistake I often see with this variation:

This happens a lot in my blitz games vs 1300+- players. They suddenly find castling difficult.

Some players just resign here, even though it's only a pawn.

It seems like they have a discovery on the queen, but the knight moves don't work. The queen can simply find shelter and black enjoys more center control.

When they instead play the "exchange" variation, then we just play a boring game of chess...

     It is white that decides how aggressive the French Defence is. Some white players opt for the safest, least aggressive lines for themselves. Black easily achieves equality early in the opening against them--something that is often difficult to obtain otherwise. Of course, it is harder for black to press for an advantage when white is playing defensively from the start, but having chances to develop a positive middlegame plan instead of concentrating on defence is nothing to be sneezed at.

Good job taking it out of context! Fischer’s quote refers to the Winawer specifically, not the whole French Defense. The full Carlsen quote is, “In my younger years I used to consider it at best a second-rate opening…”

He tends to do that a lot... find quotes, and takes them out of context for outrageous effect, and then repeats them over and over and over in the forums.

"Chess can be solved in 5 years"
"Players under 1800 blunder a piece every move"
"Anyone can go from beginner to 2000 in 1 year"

Crap like that.

Just shows. It he's arguing for something, the opposite is true. Seriously, the whole point is that an aggressive response by black is always a bit risky. But it doesn't lose by force. Often it's used to win with.

Oh sorry Mr Llama you beat me to it.

Talking of the Winawer, I used to play it from both sides, for about 6 months. The Classical (3. ...Nf6) is sounder but far more complex and difficult. I won with the Winawer but that was because my rating otb was about 1650 so that was roughly the level I was playing against. I much more enjoyed playing against the Winawer.

the french is agressive (maybe agressive is the wrong word and sharp fits better in the mainlines where white plays 3. Nc3 and can be agressive in the advance variation. If you want to play agressive in the Tarrasch 3. Nd2 you have to sacrifice soundness and not play 3. Nd2 c5.

The French has the advantage that you dont have many variations to learn compared to other mainline openings like the sicilian, the caro-kann or e5. in these openings there are many decent sidelines you have to know. the french is really about the classical, the tarrasch, the advance and the exchange  but it also has the disadvantage that besides the exchange variation you really have to know your stuff or you get crushed if your opponents knows his stuff

     Also, Fischer had a relatively poor record vs the Winawer--not as successful as he should have been vs lower-rated players playing what he said was an "unsound" variation. The most notable example was his being crushed right in his pet 4.a3 opening line by unknown IM Kovacevic (using a dated Alatorsev system). He probably didn't quite "get" the Winawer.

The word I used in post #3 above was "ambitious".