"Top of the line" - - the best (most expensive) in a given line of merchandise
Top of the line media would be the generally accepted best quality media, and thus also among the more expensive media.
Two examples that come to mind are:
Verbatim (outside Asia) also known as Mitsubishi (in Asia)
My Matshita UJ-840S drive (not 850S) hates a lot of DVD media that burn well on other drives, and only really likes Taiyo Yuden DVD+R media (8x or 16x). It doesn't like most Verbatim DVD media very well either. It's an extremely picky drive, but I'm not sure if your UJ-850S is as picky as my UJ-840S.
I would follow the advice given previously and restrict yourself to using known good media on your Matshita drive - Taiyo Yuden if you can find it, or Verbatim. I also suggest trying to burn at 6x or even 4x if you have problems burning at full speed (8x) on your drive.