It really boils down to the party you're in. If I had only one good tank and a bunch of melee who can't dodge wheels, sure I might as well make the tank bear all the burden with them tanking Garuda and Suparna. If I was in a party full of horribads, I'd go with triangle simply because it's shared responsibility and teaches all the fight mechanics while also being the safest strategy when performed right. In a farming party I'd definitely assume everyone knows the fight well and go for a quick kill, with MT pulling Chirada and OT Suparna, killing Suparna first. Even with multiple melees in party because good melees know to dodge wheels. Personally I think that you'll have more up time on the sisters (as melee DPS) by dodging the wheels and only moving through tornados once, as opposed to waiting for OT to pull the 2nd sister through the winds or moving through the tornados twice.

I really like Garuda Ex in all honesty. I just wish people were more flexible with their strategies to accommodate a wider variety of people, besides the obvious overgeared tanks and ranged DPS.