Monster or CareerBuilder? Don't favor either of them, because certain companies only commit to using one or the other. If you want access to the widest spectrum of available jobs and positions offered by all companies then use both sites frequently.
As more and more companies outsource their online recruitment efforts to the two major players, some will not take the time to pay the extra money for double job postings on the two sites. I'm sure that Monster and CareerBuilder cut deals to companies, but currently the price is steep for a single job posting at $419 for a 30-day single job posting on CareerBuilder.com (as of 9.25.2007). I don't know many small businesses that can afford to post multiple positions, so you can see why a company would only post on one site if they are trying to meet their revenue goals by limiting expenses.
Of course, another reason that certain companies only use one site or the other is if they are larger and are constantly posting available positions. I would not doubt that the executives at the job searching giants cut deals to the bigger clients under the condition that they use their services exclusively. That's just my personal view and guess as to the way the job searching industry works.
Regardless of how or why companies only post on one site or the other you need to have your resume and be active on both sites.
