Efficiency is not an issue with radiators unless you haven't much room and need a very compact one. It is the efficiency of your boiler that matters, If your radiators aren't veryefficient they will run hotter to give the same heat output as a more efficent one. If you aren't worried about having whacky stylish radiators then go for the one that gives the heat output you want at the lowest price as per Heathfields suggestion. You might need that little bit extra heat during a very cold spell.