David Cameron should rule without a doubt. He is the prime minister of UK and the people voted him into the office to make the country a better place. Queen Elizabeth is in no doubt historical important, as she carries the tradition, but she is not fit to rule. David Cameron has the leadership and abilites to lead the country and make well informed decisions that will help every party.
Like him or not, David Cameron is the properly elected Prime Minister of the U.K. Like her or not, Queen Elizabeth is the head of a family that has spent more time leading the tabloid headlines than they have spent leading a country. The idea that an 87 year old with no government experience should lead one of the most powerful nations in the world is frankly ridiculous.