[LibGDX]How to scale Images up or down to fit multiple android screen sizes

Question

I have just moved into LibGDX for mobile games and come across a problem i didn't need to deal with before with computer games, The different screen sizes and resolutions.

I have searched around for answers and try a few different things but nothing seems to work.

My code atm incorporates an Orthographic Camera and setting the viewpoint of that to the screen width and height which i receive from Gdx.graphics.getWidth();

I am trying to do this for the menu atm but it will have to also carry through to the actual game which will consist of tiles.(Tiled Sidescroller)

Current Code:

private Texture MenuBack = new Texture(Gdx.files.internal("Img/Menu_Back.png"));

SpriteBatch sb = new SpriteBatch();

float ScreenW = 1280;
float ScreenH = 720;

OrthographicCamera cam;

@Override
public void render(float delta) {

    cam = new OrthographicCamera();
    cam.setToOrtho(false, ScreenW, ScreenH);
    cam.viewportHeight = ScreenH;
    cam.viewportWidth = ScreenW;
    cam.update(); 

    Gdx.gl.glClearColor(0, 0, 0, 1);
    Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
    sb.begin();
    sb.draw(MenuBack, 0, 0);
    sb.end();

}

Im not entirely sure why it will not work. My entire aim of this is to scale everything up or down from the most suitable size so i would not have to add extra images for the few sizes that may not be popular.

Also, When performing scaling up or down, would it be better to use a stage with actors or a SpriteBatch.

UPDATE: I have tried to use viewpoints but i cannot get it to scale properly with my 1280x720 background

Thanks for Any Help