If you want a good reader, keep the LiteOn. If you want a good writer, keep the NEC. Or keep both of them and kick your DVD-ROM (that’s what I should do!)
With the firmware you’re using, the NEC can also do SL and DL +R bitsetting. Bitsetting on -R is not possible, it’s not supported by the standard. With the right firmware, you can do +RW bitsetting too on the NEC. LiteOn does it all.
If you want to use cheap media (Princo, Emtech, Infosmart), keep the NEC for sure! There is a change that your LiteOn will be destroyed beyond repair when you use cheap media on a regular base.
If you want to do PI/PO tests, only the LiteOn can do it. But when you keep the NEC, you won’t need them, because every burn is good!
I’ve been having a LiteOn LDW-411S@811S for some time and sold it because I was not satisfied. After a NEC ND-2510A, I now have a NEC ND-3500AG. I’ve never regretted the changeover.