I agree with Russ. "The Best" is hard to say since companies have different needs.
Many larger companies with multiple HR managers and recruiters, more sophisticated needs, and larger budgets prefer products such as Taleo.
Many small to mid-sized companies, with fewer HR managers and recruiters and smaller budgets find that many of the more affordable, yet still robust monthly subscription products are a better fit for their needs.
Our company offers a product called ApplicantStack, www.applicantstack.com, that is targeted to small to mid-sized business. Other products targeted to a similar audience are: ICIMS, www.icims.com, PCRecruiter, www.pcrecruiter.com, and Bullhorn, www.bullhorn.com.
Since there are many products that, at first glance, can look very similar. It's good to set your requirements, look at a product demo, look at the reference list, and then consider signing up for a free, no-risk trial of the product.