In my own opinion, the best defensive set up is when you have at least 3 of the legendary ninja heroes where Garnet is tanking and at the wings are Cobalt and Onyx. The reason is that their family bonus gives them the chance to do some minor ripost and the most aggravating is that they have a chance to dodge the attacker’s skills and the tile damage. Cobalt and Onyx at wings are deadly when allowed to fire their specials at the third charge while dodging attacks directed at them. Ideal flanks are Frigg on the left and costumed Kadilen on the right, especially more so if you have 2 nature epic troops maxed or highly leveled. But I don’t reroll this kind of defense as it gives me opportunity to test my mettle. Only with favorable boards will you be able to win with this kind of defense. Again, this is just my opinion.
But if you want to have the best defense out of the heroes you have, you have to consider your wars. If the alliance demands a certain element to be your war defense, you need to focus your resources on the tankiest hero of that element. If your alliance is doing green tanks in wars, then Telluria is your best bet. Flank her with your best emblemed legendaries with fast or very fast heroes at the wings. If your alliance is demanding blue tanks, then Krampus would be the tanking hero and you will be forced to strip Ursena of her emblems. I still think Kunchen as a viable alternative tank to Ursena and is also good during very fast wars and 5* tourneys. For yellow tanks, i see your costumed Vivica who also casts regular defense down against the enemies while healing the entire team much like Kunchen does but at a higher defense debuff of -44% than Kunchen’s -34%. For red tank, I only see your Grazul serving well there since she has tanky stats compared to the rest of your fire legendaries. Generally, you can experiment which heroes serve you well at flanks and at wings thru your default raid defense by calibrating or reconfiguring them daily or every X days or so.
But keep in mind, with the Element Charge war support still to come, all players must have a tanking hero for every element highly or fully emblemed in order to take advantage of the boost of that element during defense in that kind of war support. So far, that is the only one included as a new addition to the war supports (Undead Horde, Very Fast Wars, Status Effects Removal) we have yet to see in the live game. Maybe during this Wednesday war.