No one, whether poet or orator, ever yet thought anyone else better than himself. This is the case even with bad ones.

[Nemo umquam neque poëta neque orator fuit, qui quemquam meliorem quam se arbitraretur. Hoc etiam malis contingit.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Epistulae ad Atticum [Letters to Atticus], Book 14, Letter 20, sec. 3 (14.20.3) (44 BC) [tr. Shuckburgh (1900), # 724]
    (Source)

At Atticus' suggestion that Cicero write a speech for Brutus to give before the people of Rome. Cicero goes on to suggest this will be even more true for someone gifted and erudite, like Brutus, whose oratorical tastes and style are different from Cicero's.

(Source (Latin)). Alternate translations:

There has never yet been either a poet or an orator who did not consider himself the greatest in the world.
[ed. Harbottle (1906)]

No one, whether poet or orator, ever thought anyone better than himself. This is so even in the case of bad ones.
[tr. Windstedt (Loeb) (1913)]

There never was a poet or an orator who thought any one better than himself.
[tr. McKinlay (1926), # 104]

There was never a poet or orator yet who thought anyone better than himself. This applies even to the bad ones.
[tr. Shackleton Bailey (1968)]