Should /etc/localtime be a file or a symlink ?

As installed, /etc/localtime is a copy of one of the files in /usr/share/zoneinfo.

If I change the system's timezone, using a system-config-date, I also get a copy of one of these files.
The reasons I've seen for making this a file is that otherwise yum update might mess up the settings.

Browsing the internet, however, I get a large number of recommendations to make /etc/localtime a symlink to the zoneinfo file.
Supposedly, this helps in determining the currently active timezone. Note that the info /etc/zoneinfo is not always correct on the systems I manage.

What is the accepted best practice here ? File or symlink ? And why ?