Despite some semblance of simplicity, defamation law is complicated. It varies a lot depending on a jurisdiction, but also it is often based on fictional “reasonable person’s in the circumstances” perception. What would be this perception in every particular case — a judge would decide. In a way it is possible to say that a judge’s perception matters a lot.
This is not a flaw of the system, in fact it’s a part of its original design: laws were meant to be applied by respectable community members, to avoid abuse, excessive harshness, and to ensure that the law of the land is connected with… well, the land.
Yet, this means that not any lawyer, however experienced and prominent, is good to argue a defamation case. Such a lawyer should know and understand the community, he(she) should know what kind of a “reasonable person” would be taken into account and how much weight the judge would give to the “circumstances.” And, of course, the lawyer should know the law of this particular jurisdiction (in Quebec you cannot even call yourself a lawyer without being a member of the Quebec Bar).
All in all, this means that the right question is not “who is the best defamation lawyer?” but rather “who is the best defamation lawyer near me?” In Montreal, this does not make a huge difference: thousands of lawyers are available. But what if your case is one of a small community? Finding a lawyer with particular knowledge in defamation law yet with good ties in the community might be a challenge.