Well it depends on what you'll be OTing. Twintania doesn't require the OT take a butt ton of damage, so essentially becoming a DPS who tanks some things there's no reason not to build for STR and DET. For EM Primals both OT and MT have stuff to actually tank that hits hard so you can't build for STR/DET in that situation. Survivability is important in most fights, but there are times when Parry will be practically worthless and your damage output (no matter how small) would matter more. Plus WAR can burst down a Conflag like no one's business.

Anyway, it's pretty easy to determine BiS. Just take your main stat, get that as high as possible, stay at the accuracy cap for t5, and build your set around parry. Allagan helm, Myth chest, Myth gloves, Allagan belt, Myth pants, Allagan Flanchards, Allagan necklace and earrings, Myth wrist, Allagan ring, Hero's ring, and finally Allagan axe. There's your BiS for tanking, glhf.