The Best Metal distortion pedal i've tried was the Digitech Metal master and the Boss Digital Metalizer. Choose the Digitech if you want a more modern metal sound and also for heavier styles like Black metal, the first thing i did was to dial in the guitar tone from Burzum's album "Filosofem" :32:
The Metalizer is no longer availble new from Boss but to my ears it sounds better then the new Metal Zone, less controls but better sounding. More fat, low tones then the zone's weak bass and middy tone IMO