#1 - Bone wall. It fits my playstyle quite nicely, and is easily my favourite death card. (If SoSa weren't so OP I'd have voted for it as well; it fits my playstyle nicely as well, but I don't think it should be so strong) My favourite place for bone wall is in upped speedbows; people never seem to expect it, and alongside a couple thunderbolts or maxwell's or OE or something, it's pretty darned good.
#2 - Arsenic. Another one I like a lot, but missed being #1 because there are several other really good cheap weapons, whereas bone wall is mostly unique.
#3 - Boneyard. Not really a strong card, but tons of fun
I don't think I've ever built a competitive pvp deck with it, but I have a blast using it sometimes in weird decks for going against halfbloods, like fractal ball lightning boneyard or bonecats or something.