depends on your group, but an extra flare (from double flaring) on the avatar shouldnt make or break the fight. i prefer single targeting the dread and single flaring with swiftcast convert.

as blm, i start off the fight in the dreadnaught tower and AM over to the rest of the party after i get languishing. have AM macro'ed to a healer who isn't pushing towers with you. you can choose to start off with raging strikes and use only an x-pot on the first dread. raging should be back up by the time second dread comes out. personally, i use raging on first dread and x-pot on second, but either is fine. i wouldnt waste a potion cd on a mega-ether. that extra flare isn't needed and an x-pot does a lot more dps. if you have time for three flares on the dread, it's dying too slow.