#2
I would get a DiMarzio D Activator Humbucker and a DiMarzio YJM as your single coil.

I have heard both of these pick ups and the Activator has amazing harmonics and is very clear whether your playing power chords or single notes. The YJM is just plain amazing for clean and distorted sounds, it's mainly used for single notes.
#3
What amp?
What guitar?
What other gear do you use?

Also, be a bit more specific - name some bands who have a tone that you like. Saying that you play metal and shred is basically saying "I play everything thats heavy" and there are a lot of different tones out there in the metal world.
#4
for the single coil I think the most popular is the HS-3/YJM (pretty much same thing), and as for a humbucker you need to be more specific, like dude above said.
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