It depends on a wide variety of factors primarilty the burner used and the quality/speed of media used. Getting good meida is more important then people would think, not only for lower errors but for the longevity of your CD's.
Newer high speed burners and media usually produce more errors when burned slow.
There is no universal answer as each case is different.
BUT, if I were you I would head over to the media forum and learn how to scan for C1/C2 errors. Once you can check the errors on your discs you can try a different speed and compare.
For example on my LiteOn burner I've determied that 32x is my optimal burn speed with the media I am using at the moment.