I prefer Black Metal I guess, but a hefty dose of both. I actually prefer the bastard offsprings of both genres more than the pure ones in a lot of cases! I don't care if they are called sellouts I'd listen to them over the purebreeds any day, but I definatly enjoy those too.
I like Doom too, and to me BM is closer to Doom/Drone than DM, so I bunch those 2 together whilst Thrash and Death Metal seem more akin, and I am not a fan of most Thrash, so yeah, I listen to more Doom/Black than Thrash/Death.
The real question related to Opeth should be what is better, Prog or Jazz? Since those elements are just as important in their music as the Metal side of things! The more under looked elements when it comes to comparing I think!