Verdi on Verdi

Following up on yesterday's Traviata, I've been dipping into Julian Budder's splendid The Operas of Verdi where, inter alia, I find this nugget:

When in the years immediately following its revival which of his operas written to date he considered his best, he is said to have replied: 'Speaking as a professisonal, Rigoletto; speaking as an amateur La Traviata.

Counting only his work up to La Traviata, I'd say this is a shrewd insight. But I wonder when, exactly, he said it? Of course never did anything again with the spare elegance of La Traviata, but he did do Don Carlos and Otello and Falstaff. They don't exactly put Rigoletto to shame, but they certainly belong on at least the same level.