I use Verbatim 6x discs in my Pioneer 207MBK and LG GGW-H20L. Mine are not the ink jet printable variety, but that is the only difference.
Verbatim are known to burn well, and there are very few reports from users regarding problems of any type. They didn't score very well in the one longevity test we've seen, but real-world use doesn't seem to correspond with those findings very well so far.
Rated to 12x means that if your burner can actually burn at that speed, and has support for these discs in its firmware, you can burn at very high speed. I wouldn't advise it however. I burn Blu-ray at 4x 90% of the time, and have only tried 6x burns on rare occasions. They worked ok, but I don't have a scanning drive to examine differences between those speeds.