Double oven hands down. I personally wouldn't just own a single oven, and I would make sure that both ovens were fan ovens. I have a gorgeous Neff double, but the top isn't a fan oven, so I can't cook as well in it.
So if I am doing a roast, and my joint of meat and my roasties aren't done at the same time or the same temp, I can use both ovens. Or for instance I am doing a roast tonight and I will do my Yorkshire Puds in the smaller oven and my joint and roast potatoes in the big one.
Good luck, its a gorgeous cooker!