I think it's not a matter of aliased or anti-aliased, it's a matter of which one is better for certain fonts. I have posted a message on the BSD Forums
regarding this issue.
There are fonts at certain sizes that look better aliased, and others that look better antialiased at other sizes.
Here's a ~/.fonts.conf
file that defines these rules pretty much the same way as on Windows. I think for instance that Verdana 11px looks better aliased, and Times New Roman 22px looks better anti-aliased.