Appoint the reluctant candidate who needs to be cajoled into accepting the position because they are not driven by naked ambition, they are not over confident, they will not see dissent as personal disloyalty or feel so insecure in the post as to shut down debate. If their reluctance is not based on doubts about their ability but an accurate assessment of the difficult nature of the post and the foresight to see the difficulties that lie ahead then they will not underestimate the task or make unrealistic promises. They are more likely to surround themselves with people who have the skills and knowledge to meet the challenges and more likely to listen to them, rather than those than will tell them what they think they want to hear.
I have on many occasions suggested and encourage someone I thought would make a good appointment to apply for a more senior post. In my experience those who show reluctance do so because of their insight into the nature of the role and the difficulties they anticipate encountering are not letting ambition cloud their judgment.
They do not lack confidence in their own ability although they do sometimes underestimate the impact they have and underplay their achievements, more often than not attributing success to the team rather than their leadership. Often they balk at the management culture they simply don’t want to be that type of manager , work those excessive hours , risk upsetting a work-life balance that they think is good for them and their family.
I genuinely believe it is possible to retain your integrity and stay true to your management style in a more senior post even if that is not the culture being modelled by your boss or colleagues. Like wise I believe you don’t have to get sucked into demonstrating your commitment to the organisation by arriving early, leaving late and not taking your full holiday entitlement. You will be judged but if you and your team are delivering, and I am confident you will, then how you do it is less likely to be of concern to your boss. The thing is the more people like you go for and get senior posts the more likely the management culture is to change.