I prefer "nearest hostile" over "nearest mobile" because that way I will only attack monsters while ignoring summons. I combine it with a close paperdoll, open paperdoll macro to get the monsters to flag on me. This combination only works on CC. EC users often times attack summons and if you've ever gotten purged out of vampire form in the middle of a fight because you accidentally attacked a rising colossus you know how annoying that can be...