Check how often companies are posting job requirements. Any good website would always mention the job posting site, so that you do not waste time applying for a job posted months earlier. The relevancy and the frequency of updating jobs are important criterion.
Give preference to sites with greater interactivity. Look out for blogs, forums or other interactive platforms within the job search website.
Check out for tools offered by the site enabling better management of your search. These may include flagging off, getting job alerts and notifications, facility for easy and fast uploading of resumes and simpler management console. Check if the job search site offers something extra. That is, it goes beyond the actual services of recruitment. These may include stuff like company reviews and online networking platforms.
Ensure that you check on the above factors before you short list the job search sites to register with. The site should satisfy the basic criteria of convenience, accessibility, easy management, interactivity, safety and other add on benefits.