Which burner do you have? Others who have that particular drive may chip in and tell you which media works well with it.
And by the way, Ridata and Memorex are two types of disks I won't touch. Ritek (Ridata) is not a good choice, and you never know what you'll get with Memorex, but it will probably be crap. Buy Verbatim or Taiyo Yuden and you'll be much better off as a general rule. You can buy 8x TY at rima.com if you are in the US, and it is some of the best media available, even though some might argue that even TY has gone down some in the last year. The 8x TY works well in most drives.
If you are set on using 16x, or don't want to buy online, then you should try the Verbatims.