my favorite opening is aljechin defence.
Sicilian defense best opening for black?

There is no "best". There are a finite number of sound defenses, but there is no best.
The "Big Four" tend to have the best reputation: 1...e5, 1...e6, 1...c5, 1...c6
Then nobody has been able to refute the following, but they are more questionable than the "Big Four": 1...d6, 1...d5, 1...g6, 1...Nf6, 1...Nc6
The other 11 moves range from borderline unsound, like 1...b6 or 1...a6, to outright bad, like 1...f5.
I always tell people, the best answer to 1.e4 is whichever one of the "Big Four" leads to the positions that you personally are most comfortable with. For you that may be 1...c5. For someone else it might be 1...e5. For me, it's 1...e6.

"Larsen was one of the diehards who refused to abandon the Dragon until recently. White's attack almost plays itself ... weak players even beat Grandmasters with it. I once thumbed through several issues of Schakhmatny Bulletin, when the Yugoslav Attack was making its debut, and found the ratio was something like nine wins out of ten in White's favor. Will Black succeed in reinforcing the variation? Time will tell."
- Bobby Fischer, from his book "My 60 Memorable Games".

my favourite opening is sicilian defense
A Heroic Defense in the Sicilian Najdorf - Kids, don't try this at home! - Chess Forums - Chess.com

- time on off
- shove a ninja
- con
- rosy limo
- my rotsy bind
- clash nick off
- saveshny cough
- night orf. What’s an orf?
Now dragons I can get behind!

What if it farts? You'll rue the day you got behind a dragon!

f4 (Bird's eye opening; i play leningrad variation) is not bad; I play it almost every time as white and as black the dutch defense/f5 if opponent plays the queen side pawns and sicilian if on the king side
my favourite opening is sicilian defense