Hee, yeah. And they do have the benefit of being a) canon and b) lasting more than a season. Sort of. In the way where they aren't an actual couple.

Although Spike and Dru have been only around since the 1800s, and Adam's 400, right? So maybe he has killed more people. On the other hand, it's probably more likely that Spike and Dru were killing people on a much more regular basis and all, so maybe they still have the advantage in body count.

I bet Adam was the Immortal from that one episode of Angel. *sage nod*