The higher the output should be the higher the input must be-nothing comes for nothing.So trying to get a lot of kW out of a radiator needs a either a high running temperature or a fast pump setting. Both will cost permanently money. From the day you buy them untill you leave the house with the feet first. If space allows for it then the cheaper (because more passive) solution is more economical: large heating surfaces fed by low flow temperatures, similar to UFH, wallheating. It might also be more cosy because of less candle flickering, curtain movements, noise.