On Okinawa, butter and margarine aren't even used: the only fat they use is oil, and especially rapeseed oil. It contains very little saturated fatty acids and Omega 6, which are particularly bad, and it contains 'good' monounsaturated fatty acids.
Studies carried out over decades have concluded that the healthiest way is to stick to olive oil for cooking (without smoking it) and rapeseed oil for seasoning. Always go for virgin, organic oil in opaque glass bottles - never plastic ones! If you have 2 tablespoons of rapeseed oil and three portions of oily fish per week, you're getting the right amount of Omega 3 in your diet.