My favourite is Martin Heidegger. He is, in my mind, the model of what a philosopher should be. Every question he investigated he considered deeply important and refused to accept any shallow answers, even despising the shallowness of his contemporaries. He investigated almost any topic, since everything made him intellectual curious. Finally, he never rejected an idea just for belonging to a system of metaphysics he didn't agree with; he was open to the breadth of truth. It is difficult, even amongst the great philosophers, to find one accomplished in both breadth and depth.