Obviously it's impossible to select a perfect line from a poem, but it's a fun and interesting test of one's emotional sensibilities and technical sensitivities. Mine are not arbitrary, though they're lucky to be picked ahead of one or two other contenders.

If I had to pick a perfect line from a poem, I'd go either for Shakespeare's beautifully cantilevered line, "I wasted time and now doth time waste me," spoken by Richard II, or instead Marlowe's exquisite iambs in Faustus's melody of damnation: "Was this the face that launch'd a thousand ships / And burnt the topless towers of Ilium?"

These lines, methinks, can never be improved upon! So, come on, what do you think is poetry's "perfect line"?