Hi wldctj8, welcome to CDFreaks!
As chas0039 said, it depends on the media, the drive and the firmware.
As a general rule I burn both 8x and 16x DVD media at 8x in my burners, because the quality is almost never worse at 8x than at higher burn speeds, but even at 12x the burn quality is often slighty worse or there's a slightly higher risk of a bad burn.
Because of some compatibility problems, I burn at 6x in my Optiarc 7173 drive and at 4x in my NEC 4551 drive.
You will seldom if ever go wrong with burning 8x and 16x DVD media at 8x in current desktop burners. In laptop burners I suggest burning at one step below maximum speed.