Toss-up between the PX-712A and the DW-1620. I've used the Plex longer than any other DVD drive I currently own and have burned more media than with the other DVD drives combined. It rips fast, writes fast, and doesn't fail me. The BenQ's freaking amazing with +R media, so I use it a lot, too. I hate burning CD-Rs with it, though.
The NEC is a all-around solid, impressive drive, but two things bother me: you have to flash it with modded firmware to set booktypes or remove the reading speed limit... and it has that CHEAPASS looking eject button. It's just a reliable, boring drive.
Drives I liked but gave away: ND-2500A & ND-2510A, PX-712A (took it back, though :)).
Drives I threw in the trash bin: Litey SOHW-812S.