Originally Posted by
LineageRazor
Honestly, I'd say it's probably better to look for what the other DPS is targeting, and attack that. If you're not using aoes, it's best to kill a target as fast as possible, and the best way to do that is to focus on the same target as the other DPS. Additionally, by focusing on the same target as the other DPS, you increase the chances that that monster will die before either DPS gets enough hate to overcome the tank's distributed enmity.
A tank, on the other hand, is going to be rapidly switching targets for pretty much the entire fight in order to spread their enmity-building single target attacks across as many mobs as possible. If you target what the tank targets, you will be switching targets the entire fight as well.
When burning down targets one at a time (rather than aoe on all the targets), it's more efficient and safer to target the same mob the other DPS does. (Also remain aware that the other DPS might apply DoTs to several mobs before settling on one - as ACN 50, I'm sure you do this yourself, but other classes with DoTs may do this as well!)