In my opinion Verbatim 16x media (MCC 004 and MCC 03RG20) has always been as good as or better than Verbatim 8x media (MCC 003 and MCC 02RG20) for burning at 8x speed or slower, and when burning at 12x there’s no contest at all - 16x is far better.
That being said, I have had some very good burns with Verbatim 8x media, +R as well as -R, with most drives preferring +R over -R.
I’m not convinced that there’s a real answer to that question, other than “it varies from batch to batch”.
I have had very good burns with all three types, although I have only burned a few +R MBI. For me the best Verbatim 8x DVD+R batch has been Made in Taiwan by Prodisc, but the difference has been marginal.
I have only had CMC made Verbatim DVD-R (MCC 02RG20), and they have been of variable quality. The best of these burned in my NEC 3500 have been very good, but I have found that some burners have a difficult time burning this media with good quality.
If I had to choose between 16x and 8x Verbatim media, I would choose the 16x media without hesitation, unless I had an older burner without proper firmware support.
I haven’t tried any Verbatim 8x Pearl White media, however.