I'm re-watching the Fairy Tail anime from episode 1, and although Grimoire Heart and Tartaros was stronger than Oracion Seis, The Oracion Seis actually beat Fairy tail. They also beat Lamia scale with Jura and Blue Pegasus with Fairy Tail. Now Fairy Tail members were stronger when they fought GH and Tartaros also they fought with more passion against Tartaros because of what they did to Erza and Gray fighting Zero. So who do you think was the best branch of the Balam Alliance?
I think if the three of them fought Tartaros would win but Azuma and Cobra could most definitely hold there own.