I listen to metal. actually i listen to stuff from jazz to death metal. I also have in my garage a JL W1, W3v3, W6v2, Kicker L7 and used to have others such as Infinity reference, Punch.....etc. All are/were 12's.
In all honesty, the box will have way more difference than your sub of choice. I got listening experience going back to 1993, much of it now just a fading memory and everyone has an opinion like they got an ahole. But its my opinion that most subs in general do the basic job of putting out bass for any kind of music. its the box that seems to matter the most.
I'll get a lashing for this, but accuracy is way over rated imo. its not exciting and audiophiles listen to boring. i like some excitement in my music. whether a kick drum has a slight "blum" at the end of it or whatever, i certainly would never notice..especially in a car while driving. So thats a choice you have to consider when selecting a box type and sub. not all cheap subs are inaccurate though. i never heard one in a proper box that i would call inaccurate to the point its ruins the music either unless it was an 8" underpowered or something.
Of all the subs i have or had. i can't pick a single one that i would say worked best with death metal for instance. Even my old Jenson's from 1993 handled Cannibal Corpse just fine and Pantera too. All i can say is the W6v2 can handle twice the power and seems more resiliant to being stressed than many of the other subs i've had. My L7 also seems to still perform well when pushed to loud levels even without enough amplification in a proper box.
So if you like it very loud and don't plan on using lots of watts, buy a decent quality sub so it won't sound like a racoon's head being beaten against a tree trunk. Plenty on non mainstream subs out there for decent prices that can do that too if you want to be in the cool.
Ported seems to have worked well for me. But i don't like the 32 hz tune so many here seem to like. I don't think most music even really goes that low, especially if its compressed. I prefer 35-40hz. But 32hz> to sealed does seem to do a bit better for rap that has so much consistant variation in bass.
I never noticed Sealed to have any more benefit for metal, the sound is more subdued, less exciting. doesn't hit any harder from what i can tell. (again the box design correctly) BP can work but only sounds decent if its tuned really low and most commercial packages are tuned too high and it will make the fast pace of metal blur too much together. That 35-40hz tune seems to be about perfect for metal music.
Size of subs and box is an issue for you to decide. I got groceries to get and a life to lead, so i can only use one 12" sub. A couple of under seat subs in addition to it aren't really too bad if you really want more bass and are tight on space.