According to OC-Freak, the 812S has better writing performance than the 811S. Also, it seems that there are fewer reports of 812S problems than there are reports of _51S problems, and there are fewer _51S problems reported than _11S problems.
So it seems that LiteOn is slowly moving towards resolving their issues. Personally, I'd recommend the 812S. NEC has good writing quality to start with, but terrible support (even worse than LiteOn's). They haven't released new FW, newer media that's come out (like 8x -R) are unsupported in the NEC, and features like bitsetting aren't being added by NEC. If it wasn't for Herrie's efforts, doing the job of improving the NEC firmware that NEC itself should've been doing, I don't think that there would be nearly as many people singing praises of NEC.