The best opening for beginners

The Vienna System ( For White )

It is no surprise that the most common of all first moves in chess is probably 1. e4 e5
Especially in the beginner level, it is the most common move that we can expect. That is what brings me to the Vienna system. Not a whole lot of beginners are aware of openings. Hence if you open Nc3 instead of Nf3, this really throws off a lot of your opponents. They might just make a blunder right here. If not and they play Nf6 we have the

The Vienna Gambit

Now if you just play f4, you are really putting some unforeseen pressure to your opponent. If they accept the gambit, you move your center pawn attacking their Knight forcing them to retreat thereby impeding their development and taking control of your center.
Even if they decline, you have a fair advantage as you now control more of the center than your opponent giving you an edge ( if you don't blunder it away) for the middle game.

Being a simple opening, it probably will stop working as your ELO increases, however for the beginner level I feel that it is quite a straight forward and relatively easy opening to wrap your head around.