Attorneys decide what cases to take based on any number of factors.
An attorney may have a personal preference for certain types of cases, or he may be employed by a firm that has chosen to specialize in a certain area of the law.
There are also different roles attorneys may take within law firms.
An attorney who is "of counsel" often holds a largely symbolic consulting position, or is helping on a case but is not the principal attorney of record. Some attorneys work only as trial attorneys, and some attorneys do not do trialwork.
Because not all attorneys handle types of cases, a person in need of legal representation should determine what area of law is relevant to the dispute and seek an attorney who can and will represent him.