Best chess opening for black ?

At your level you can play anything and be successful.

As for what opening is "best". Your opening choice should be based on what types od middle games you like to play.

Asking someone what opening is the best or what you should play. Is like asking someone what your favorite food is.

Which is easiest for beginners

Opening principles.

You should definitely learn how to play the Fried Fox Defense.

Was this video an April 1st joke or what?

I don't think so but it's still an entertaining opening. This guy has a few videos like this.

Another great opening for black is the Mosquito Gambit. When I first started playing chess, and before I had started learning principles and openings, I played something similar to this.