I can't say best since it really depends on "what metal" and "what guitar" we are talking about.
My choices are
1) PATB2 for Basswood and Alder. Well balanced, lovely harmonics, tracks fast and has serious punch. The best sustain and bendings in the bunch.
2) PATB1 in LP. Nothing kicks as much butt as that. Heavy, punchy. It tracks well and is not muddy. Till Drop C it holds very well. Not suited for fast stuff like Modern Thrash or Progressive/Powermetal. But everything else just fine.
3) Full Shred: Best definition, very punchy and articulated with the right height/Screw adjustement. Also perfect for 1 Hum guitars. Kills in LP, or other Mahogany guitars. Lacks lows in Alder or Maple, sings in Hi-end Basswood, lacks character in cheap guitars. Nothing in Duncan Catalog can cope with Low tunings (C and lower) as good as FS does. A very special Humbucker.
These are my Favorits.