Sockets or Balls? Or heck Axles?
The 2001-2003 heads, the 2004-2008 heads, or the 2009-2016 heads? Mind you, the glatorian, HF, Brain attack and okotan heads are all very similar in my opinion hence why I am clumping them together.
I personally will always prefer the 2004-2008 heads as I felt they were a bit more versatile.