Both butter and margarine are useless, empty calories. No vitamins and minerals. There's a daily budget of calories, and it's better to spend it on foods with nutrients, not just pure fat or pure sugar. Better fat sources are whole foods - seeds, nuts and maybe animal foods.
>There is even halvarine, which is twice as bad.
It's a good option. Still has taste and feel, but less empty calories, and you can spread only a thin layer, easier than with butter.