The reason Christmas trees topple so easily is because their base is so small. Anything making small contact with the ground relative to its size is going to be fairly unstable. It only has to be pushed past its edge of contact with the ground before it starts to tip over. Likewise, an object will tip over more slowly when it's center of mass is further away from the pivot point. That means the menorah, with the higher center of mass, will be easiest to control and easiest to juggle.