Ive found that burning DVD's for reliability, burn slower than the rated speed.
At the moment I'm using 8x discs, and for backups I prefer to burn at 4x. I've always found I've got a better reliability ratio this way, going back to when I first got a CD burner in 97.
Also, Matt's right, Datawrite are a leading brand, but rather than look just for the brand of disc, look for the right dye. This is key to how well the data can be read.
One of the best dyes is the Ritek dye, and *some* datawrite discs use it (most, but not all).
At the last check the Ritek G-05 dye was the current flavour of the month. The preceding G-04 being the best dye of its time.
To check which dye your discs are, get a free program called DVDIdentifier (I think it's on cdfreaks website or something like that, a quick google will bring it up no doubt).
It tells you all about the blanks you are using.
Also try not to burn to brimming capacity, as reliability tends to wear off towards the edge of the disc. Not only due to the manufacturing, but also, this is the edge of the disc, where you're more likely to get fingerprints etc.
I tend to just throw on what fits really, but just bear in mind to be wary if I'm filling it right to the edge.
Regards