I'll be honest, I love every kind of metal, maybe except some Grindcore (and I'm really starting to get into it as well).
Bring me Thrash, bring me Death, bring me Black... I love Power Metal (like Helloween, Hammerfall, etc), I actually like some NWOBHM, like Iron Maiden, Venom, Motörhead; I totally love the classic age with Led Zeppelin and Black Sabbath, and I'm a particular big fan of Mercyful Fate/King Diamond.
If I had to choose only one subgenre of Heavy Metal, I would choose Thrash, because I found it the most complete. I could not live without Slayer, Destruction, Razor, OverKill, Kreator, Tankard, etc...