How to enable Antialiasing in Finder's preview column and QuickLook?
My solution is to just use a different QuickLook generator. My generator of choice is qlcolorcode. Antialiasing works perfectly well with it and it'll even highlight source code files—which is its main purpose.

There is one bug, however, that if you are dealing with any directories or files containing a ' (single quote), there will be no QuickLook available for it due to the way the generator sends the path to the highlighter program.

Another downside is that the filename will not show in the QuickLook window. Instead, it will just say "Source file". It also will not work on textClipping files.