Comparison between best defense moves I am a novice player. I have just come across the Sicilian defense on the Internet which is also stated as "aggressive defense". The French defense (1.e4 e6) also is good. Does the French defense cramp Black's position in the midgame as a result of which it is considered next to Sicilian ? Because I find the French defense to be structurally more organised than the Sicilian.
I'm not certain what you exactly mean with it is considered next to the Sicilian. However, first of all, I would like to state that the Sicilian Defense is not always aggressive. It depends on the line you play. Often, if White castles Queenside, the game becomes very sharp. However, if White castles Kingside, the game often becomes less sharp.

The biggest problem with the French Defence is the development of Black's White Squared Bishop. The French has either very sharp lines and less sharp lines, such as 1. e4 e6 2. d4 d5 3. exd5 exd5, known as the Exchange Variation.

But in general, both openings can be really aggressive. You could take a look at:

For the Sicilian Defense:

Sicilian Defense, Dragon Variation, Yugoslav Attack

Sicilian Defense, Dragadorf Variation

Sicilian Defense, Najdorf Variation, English Attack

And for the French Defense:

French Defense, Winawer, Poisoned Pawn Variation.
French Defense, King's Indian Attack.

Again, I'm not sure what answer you're looking for, but I believe that these (aggressive) lines may be very helpful comparing them. Seeing games (especially of higher-rated players, such as GMs, makes the opening-ideas a lot more clear, so I suggest doing that.