$ connection-real_escape_string () or mysql_real_escape_string ()?

I'm doing a login, and in my php, to escape characters I do not know if it is advisable to do with mysql_real_escape_string() .

<?php
session_start();
$conexion = new mysqli("localhost","username","password","DB");
if (!$conexion) {
    die("Error al conectar con la base de datos ".$conexion->conect_error);
}
$consulta = "SELECT * FROM login";
$resultado = $conexion->query($consulta);
if($resultado->num_rows > 0){
    while($row = $resultado->fetch_assoc()){
        $usuario = $_POST['texto_login'];
        $usuario1 = mysql_real_scape_string($usuario,$conexion);
        $contrasena = $_POST['contrasena_login'];
        $contrasena1 = mysql_real_scape_string($contrasena,$conexion);
        $contrasena_sha = hash("sha512", $contrasena1);
        if ($usuario == $row['Usuario'] && $contrasena_sha == $row['Contrasena']) {
            $_SESSION = $usuario;
            echo "ok";
        }           
    }
}
$conexion->close();
?>

or

$conexion ->real_escape_string()

<?php
session_start();
$conexion = new mysqli("localhost","username","password","DB");
if (!$conexion) {
    die("Error al conectar con la base de datos ".$conexion->conect_error);
}
$consulta = "SELECT * FROM login";
$resultado = $conexion->query($consulta);
if($resultado->num_rows > 0){
    while($row = $resultado->fetch_assoc()){
        $usuario = $_POST['texto_login'];
        $usuario1 = $conexion->real_escape_string($usuario);
        $contrasena = $_POST['contrasena_login'];
        $contrasena1 = $conexion->real_escape_string($contrasena);
        $contrasena_sha = hash("sha512", $contrasena1);
        if ($usuario == $row['Usuario'] && $contrasena_sha == $row['Contrasena']) {
            $_SESSION = $usuario;
            echo "ok";
        }           
    }
}
$conexion->close();
?>

Actually, I do not know which one to use, since the official PHP page says that the mysys_live_string () 'is the previous version 5.5.0 and 7.0.0, and actually, I use the mysql and it works well for me , that is, it protects me from basic sql injections. Also in my case I use mysqli for connection to the database.