Being an owner of a BenQ 1620 hopefully this helps you in your final decision.
I ordered the BenQ based on the great reviews that all commented about the top notch burn quality of the drive. So far this drive has only been burning Fuji made in Japan Taiyo Yuden DVD+R media and burns are consistently rated as 95-98 for burn quality using the Nero Disc Quality Test with their CDSpeed application.
There was a patch recently released for the 1620 that removes the riplock and allows the drive to read DVD+/-R and +/-RW media at 16x. The drive also reads dual layer discs at a blazing 16x now as well.
After the patch was released a few folks did tests to verify that the drive was still copying discs bit-for-bit perfectly using DVD Decrypter and the results were perfect bit-for-bit copies. We verified this by using MD5 checksums on the final disc images.
I'm a big fan of Plextor (own a 121032A CDRW drive) but just couldn't justify the higher price of the PX-716A over the BenQ 1620. for the price of the 716A, you can pick up a 1620 shipped to your door (check www.newegg.com) plus go out to Best Buy this week and buy 2x 50 DVD+R spindles at $20 a pop for a grand total of $100. That's 100 DVD media AND a top of the line burner for the same cost as the Plextor.
People always talk about Plextor's high quality but the truth is that their quality isn't what it used to be, imho. Too many of my friends have purchased Plextor drives recently and had problems with them, one with a PX-708A and the other with their 24x10x48 ATA CDRW drive.