You should aim for a couple of historians from each of the four main schools of historical thought:
- Classical (Herodotus, Thucydides, Tacitus)
- Empiricist / Scientific (von Ranke, Elton, Evans, Windschuttle)
- Relativist (Carr, Vincent)
- Postmodernist (Jenkins, Derrida, White)
BTW, almost every question about "What is History?" comes back to the same essential elements: the differing opinions of the above schools on the topic of whether history should (and can) be entirely factual and based on evidence, or influenced by the perspective of the historian. You'll notice this applies to questions about "aims and purposes of history", "the influence of perspective on history", "changing approaches to the construction of history" and almost everything else you can get asked.
If in doubt, check the
syllabus to see what the main focuses are. The 'five key questions' on pp. 12-13 are the central element of the course.