My favourite is Battlemaster.
I like grand marshal/high warlord for the oldschool power they have.
Also powerful titles for me are justicar/conqueror - of the alliance/of the horde cause they 're showing experience (so far i haven't seen any person with those without having a descent knowledge of their class and of pvp).
And i respect the titles of any gladiator before wotlk with an exception of ppl who will go gladiator in s8, cause i think s8 was the only balanced season in wotlk.
I don't like Pve titles exception in Twilight Vanquisher who is quite badass!!!