which is the best response to e4?
Best for who? Best for what?
The move that's "best" for a 2100 player who wants to avoid a draw isn't going to be the same as the move that's "best" for a 1200 player who just wants to complete his development and get castled.
I like 1. ... c5, but then I'm prepared to enter this sort of craziness:
https://www.chess.com/daily/game/200865884
There are many good choices.
I like to play classically with 1...e5 and against d4 1...d5
Classics were discovered first because they're the most logical (control the center, develop your pieces, etc), and they're still played in every top tournament and world championship match.
But many other openings are good and played by top GMs too. People say to start with classics like the queen's gambit declined and Ruy Lopez because they help to teach good fundamentals like center control, piece activity, and king safety.
But sometimes people aren't aiming to be very high rated, and just want to survive the opening with very little effort. Facing 1.e4 as black, 1...d5 is a low theory, solid choice. Some people like to do a Pirc/KID setup against everything (d6, g6, Nf6, Bg7) but these openings have a lot of theory to them.
which is the best response to e4? I like c5 but i get stuck in development.