First choose the series. There are three with multiple epics available. Worth noting is that Frankenstein's Family and Polychrome Heroics both have chains of poems where posting one will unlock its sequel for release upon sponsorship or selection as a perk. After you pick the series, you'll get to vote on which specific poem you want.
Gothic fluff -- 3 epics
Historic fantasy -- 2 epics
Superhero fantasy -- 10 epics
Which series should get the free epic?