My personal experience of the Pioneer drive is that while it is very capable of reading even badly scratched discs, and even of ripping them to disc, it has major problems with "cheap" RW media. I was unable to erase or record to Datawrite 1X -RW media and -RW media, although erasable and rewriteable, displayed freezing and skipping in my dvd player. My supplier gave me a full refund after 3 weeks of using the Pioneer because of this, no questions asked.
The NEC, on the other hand, is less than sympathetic towards damaged discs but can erase and rewrite RW media with no problems resulting in perfect playback on my dvd player. Even scratched RW's display no playability problems.
My advice: If you do not intend using RW's, go for the Pioneer. But remember to use good quality media (I use only Ritek media and had no problems with this). If you intend to use RW's, go for the NEC and don't worry about media compatibility. Mine works with any old crap I throw at it.