Actually if you go to wikipedia and look up humans it will say that orcas(killer whales) are also one of the nine species who have passed the mirror test! Also the orca has the second largest brain in the world and of the cetacean family after the sperm whale. So I would say the orca is smarter or at least equal to the dolphin.
An Orca (aka Killer whale) is a dolphin. It is the largest of the dolphin species. So the answer is neither.
I would say dolphin because they are one of a very few animals who recognize themselves in a mirror where as a killer whale does not.