As a kitchen designer in training, its hard to say which is best. I personally, would have 2 single ovens side by side, a micro combi oven and a steam oven. I often find double ovens quite useless because if you're cooking for a dinner party, you dont really need to be grilling anything in the top, and thats usually what they are, just grills. Although Neff have a double oven with fans in both ovens, which is useful, but i think its just down to personal taste, how much cooking you do, and the space limitations.