In my opinion the best way to snap aggro is to simply prepare. What I personally do when picking up the adds in Garuda is to preload the first skill in my bread and butter combo. When Garuda screams DIE DIE DIE, it signals that the adds are going to spawn shortly. I run over to her, do the first skill in my combo, then when the add spawns I run over there and do the second hit, then when the add becomes mobile (they're frozen for a second) I hit with my third skill and start pulling the add towards its position.

You do insane snap aggro by immediately doing your combo, making it impossible for DPS to pull the add off you, and you should lose no time if you do it correctly.

You can do the same thing on Titan Ex by using the first skill in your combo on titan just before the adds spawn.