Best web server for serving static content ?

Any web server will do the job, but if you are looking to improve performance then try nginx or Lighttpd.
They consume very few resources compered to Apache for the same workload and are much faster at processing huge traffic loads, plus both of them are asynchronous server unlike Apache.
Though, if you only want something for your static assets then just host them on a Amazon S3 bucket there by avoiding the need to run a web server in the first place.
As most of the time Amazon S3 will outperform your own servers.

There is no such things as "BEST"

 

When it comes to web servers usually the question would be "Which can handle the most traffic?"

 

Since you seem to want to serve some static files, I don't think traffic is your main criteria here, so honestly any web server will suite you just fine.

Apache server http://httpd.apache.org/download.cgi