I would choose a firewall based more on the security features that you want and any independent evaluations available for the firewall (such as NIAP [National Information Assurance Partnership] Common Criteria evaluations), rather than throughput. Most vendors have different models of the same firewall that are applicable to different line rates, so finding one that meets your needs should not be a problem.
Stateful inspection firewalls definitely have their place and should be considered. However, port-filtering and proxy-based firewalls also have their uses. It all depends upon what you are trying to protect and what you are trying to guard against.
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This was first published in May 2003