I tend to abide by target of target as a gamepad user. If the party is all over the place in terms of what they want to do, I sometimes use a DPS for target of target, then burn that enemy down sooner, while watching my hate to make sure I don't overtake the other DPS or best case, overtake the tank.

From a tank perspective, if an enemy's position is key (its AoE) and such, I may just use my enmity bar to determine which enemy or enemies need to come back to me. If a few GCDs won't kill the DPS and I have to make the choice of recovering hate against a DPS hero or making sure I have hate on the remaining enemies, I'll choose the latter.