Who make the best Scrum Masters? First off there are several roles that make a risky proposition for Scrum Master…
People in authority – Leads and managers make poor Scrum Masters in my opinion. People tend to report progress to management and worry that they are being assessed. This scenario can work but it very much depends on the team’s relationship with their lead(s) and how your organization assesses performance in general.
Project Managers – I actually know some PM’s how have become very successful Scrum Masters (Mitch Lacey for instance). But there’s a lot to un-learn here. Project Managers have spent years running projects and organizing people, rather than facilitating teams that organize themselves. Incidentally, many A-type personalities fall into the same trap. It’s hard for them to not try to control the team.
Product Owners – There’s a clear conflict here. The Product Owner is trying to get as many features into the product as they can. The team is trying to make reasonable commitments that they can meet. The SM is trying to facilitate that process. Making the Product Owner the Scrum Master is a clear conflict of interest.
Offense vs. Defense
In general I like to think of people as either on offense (trying to get as many features into the release as possible) or defense (trying to make realistic commitments and be sure they meet them). This is both role and personality driven. In general you want someone on the defensive side as Scrum Master and you don’t want to have people fulfill roles that are on both offense and defense.
So who would I pick? If I were looking for a Scrum Master I’d try and pick one of the more experienced team members who has the team’s respect and is prepared to spend the time investing in facilitating teams.
Here’s a talk by Mitch Lacey on some of the general issues with mixing roles in Scrum. It’s worth a read.