I've been grinding exclusively frontline for pvp so my opinion may not apply to CC, but:
- Nearest enemy with the lowest HP, or whoever everyone else wants to jump (besides PLD/DRK with invuln).
- Nearest squishy/ranged. If multiple, I personally prio dancer because of their LB, especially if they have a competent team that knows how to crush us if used.
- Nearest melee DPS. I try to prio the samurai if I feel like my team will get the memo to crush them before they crush us, otherwise I try my best to avoid them or save them for last, especially since even using an AOE on them by accident can trigger their one-shot.
- WAR/GNB.
- PLD/DRK. For the love of god, please just ignore them unless we can pick them out from their team. I can't count how many teamfights that have been thrown because my team wants to play around with either of the two while they have invuln over literally anybody else around them. They aren't actually that big of a threat by themselves, please just take out the squishies around them, especially when they CAN'T be TOUCHED.
Of course, this may change depending on who has BH and who doesnt, but frontline in particular also thrives off of numbers, so you're always better off picking them apart when you can rather than constantly chasing down BHs and throwing yourself into a sea of enemies.