The amount of sites (both free and paid) offering to post job openings keeps growing. Free or paid is not a good criteria to judge quality by, as many paid sites just take jobs from other (free or paid) websites and aggregate them just to get better traffic from search engines.
When looking for a place to post a job opening, what criteria are most important in finding the best candidates? Are sites (like Stackoverflow Careers for programmers) directed toward the audience you want to fill the job more effective than aggregation sites (like Monster.com)? Is it better to advertise to a wider audience, or to focus on a single site to post all job openings? Does it depend on the type of position? What criteria should an employer use to judge the effectiveness of these postings?
Although, it can be a general question, but my focus is on teaching and education jobs!