As far as Wah pedals are concerned, I'd wait for the Zakk Wylde Signature wah by Dunlop...it is supposed to be released soon.
I use a Morley Steve Vai Bad Horsie 2 Wah. It has a boost function that can raise the volume and the drive to a preset level. I don't play metal in my band, but when I play the harder rock stuff, or if I'm goofin' at the house on some metal stuff, the Morley sounds great to my ear.
The Fasel capacitor used in the old vintage wahs is generally considered to have a warmer, more musical tone to it. Mind you, it may not be the best tone for outright metal though. The subtleties of the tone may be lost in that wonderful Recto wash of TONE.
My best advice to you is to drag your amp (your whole rig, actually) to wherever you can audition these different pedals. You will never really know how they work until you play them through YOUR setup. Just pick the one that makes the most goosebumps pop out.
RB