Jonathan Steinberg's biography of Bismark looks fascinating. This point at the end of the Times review (made by one Henry Kissinger) grabbed me:
The second caveat concerns the direct line Steinberg draws from Bismarck to Hitler. Bismarck was a rationalist, Hitler a romantic nihilist. Bismarck's essence was his sense of limits and equilibrium; Hitler's was the absence of measure and rejection of restraint. The idea of conquering Europe would never have come to Bismarck; it was always part of Hitler's vision. Hitler could never have pronounced Bismarck's famous dictum that statesmanship consisted of listening carefully to the footsteps of God through history and walking with him a few steps of the way. Hitler left a vacuum. Bismarck left a state strong enough to overcome two catastrophic defeats as well as a legacy of unassimilable greatness. Nevertheless, "Bismarck: A Life" is the best study of its subject in the English language.