I have also tried both. Originally ordered the Poetic because the OEM was out of stock.
Poetic: came fast (shipped to Canada, sometimes stuff takes forever) and I was impressed with the fit. Someone at the gym accidently pulled my phone down off the top of a 6 ft locker and dropped straight to the floor. No visible damage to phone or bumper. After a week of use though, I had the seperation issue that others noted with earlier batches.
OEM: Ordered this from shopandriod.com when the Poetic let go on me. The quality and fit of the OEM if second to none. The bumper is clearly designed to go with the phone both visually and dimensionally.
After I ordered the OEM, I heard about the replacement warranty with Poetic. Amazing customer service, very fast to ship a replacement at no cost to me and I did not have to ship back the faulty one.
Verdict: I love the OEM look and feel, but for protection (which honestly is minimal for both) they are equal. If you are watching pennies, go for the Poetic. If you are looking for the sleekest, I would say OEM (but you pay for that premium).