I don't have that much verse by heart since that kind of work was never done in school (what a waste of time!), so when I do quote something from memory it is always the most familiar. But it seems to cause the greatest confusion to my editors. Last year it was 'To take arms against a sea of troubles.' Today already it's 'Exegi monumentum aere perennius'--I put it in English, of course. This carried back queries of what translation it was from and, most oddly, the desire to associate it with a page number.