Originally posted by tomtom232
I would recomend the sicilian defence Najdorf variation.
I don't mean to be a pedant, but advice like this isn't really helpful, because it presumes that white will choose to play an open sicilian. A more appropriate answer -- if a question like this deserves an answer at all -- would be to say to play 1...c5.
That being said, I don't know your true rating OP, but I'll assume you are a beginner, and I wouldn't get too concerned with opening theory and lines. I suggest mirroring white's move 1.e4 with 1..e5 and sticking to the main opening principles (fight for the centre, develop your pieces, don't make unnecessary pawn movements, don't unecessarily move a piece more than once, castle early, castle often).
If you insist on studying openings in more depth, then I will mention that the three most popular defences to 1.e4 are 1...c5 (Sicilian defence), 1...e5 (Double Kings pawn), and 1...e6 (French defence).
Of those three, the Sicilian is probably the sharpest and most complex. You could experiment with these openings and find one that is comfortable for you.