what is best opening for white n defense for black


There is no "best". There is a finite number of good responses.
For example, against 1.e4, you have 4 good responses. 1...e5, 1...e6, 1...c5, and 1...c6. The other 16 responses are all weaker to varying degrees, like 1...d6 is better than 1...b6 which is better than 1...f5, but they are all weaker than the 4 responses given initially.
Against d4, the QGA, QGD, Slav, Semi-Slav, Nimzo-Indian, Queen's Indian, Bogo-Indian, Modern Benoni, Classical and Stonewall Dutch, Kings Indian, and Old Indian are all better than the alternatives.
White - e4, d4, c4, Nf3 are the strongest. Tier two openings are b4, Nc3, f4, b3, g3. Other moves are weaker.
But no one of these is best. Depends on your style of play and thought process.
For example, The Sicilian and French are more aggressive than 1...e5 or the Caro-Kann. They lead to quicker development for Black, but the French and d6-Sicilians have a bad Bishop (light and dark respectively) while your e6-Sicilians tend to lead to a space disadvantage. The Caro-Kann is very slow and you lag behind in development, but neither Bishop is both bad and inactive, like in the French.
1...e5 the focus is often on keeping the strong point on e5 and less about attacking the White King.
It's a decision you have to make. I play the French, but that does not make that the best for everybody! There are plenty of strong Sicilian, Caro-Kann, and 1...e5 players out there! But I can absolutely assure you they are all better than 1...b5 or 1...f5, both of which hang material