Saul Friedlander states that "a man above all: Hitler" started the process and that it was not "generated in the machinery of Nazi and SS administration". That is quite normal he argues in that direction, given he is an "intentionalist".
The opposite quotes can be found as well 
 Christopher R. Browning, The Path to Genocide: Essays on Launching the Final Solution, Cambridge University Press, 1995, p.87 writes 
"Martin Broszat and Hans Mommsen, however argued that [the mass murder] occured without any specific and comprehensive Hitler decision or order. The system's automatic mechanisms for 'cumulative radicalization' more than Hitler's ideology and leadership explained the origin of the Final Solution"  
 Gerald Fleming, Hitler and the Final Solution, University of California Press, 1987, p.II writes 
"It may be tempting to state that each approach has its merits and to seek an synthesis between the two positions. In fact, functionalism, which stresses the dynamics of a system instead of a central role of a leader, fits better in many ways within the mainstream of modern historiography. The image it offers of Nazism is more 'normal', easier to explain: any group can stumble hapharzadly, from step to step, into the most extreme criminal behavior. Responsibility remains obviously; but it is more deluted, more nebulous, because of the very automatism of the process, its outcome unforseeable, and because of the absence of real premeditation as well. Intentionalism at the other hand asserts that the course of action was in some way planned. This latter view gives Hitler a predominant role, but it also implies much greater awareness at various level; whereas functionalism pushed to its logical conclusion, gets very close to denying that Hitler had accurate knowledge of the Final Solution. It leaves most of the operation to subordinates agencies - in a nutshell, to police terror."
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