Recordable DVDs for backup. Hmmm. After a few years of religiously tracking the best brands and best drives, etc., I gave up on them a while back and simply back up to hard drive now. From memory, which was current as of about 2 years ago:
All things being equal, DVD+R is a much better standard (by design), for high-speed recording (which all recording is now), and is way better for multi-session usage if you're mad enough to go down that path.
Recovering data is easier from a bad single-layer DVD than a bad dual-layer DVD. It's easier from DVD+R than DVD-R.
The dye used in a recordable media contributes to the overall quality. First-generation cyanine has a life of around 5 - 10 years, as a chemical. Second-generation is around 50 years. Azo is maybe 60 years. The resulting media has a life from 1 - 60 years.
On recordable CDs, you can tell what the dye is by looking at the reflected color of the disk. You can't do that with DVD since most of the manufacturers have worked hard to make the colors look the same.
In the past, Taiyo Yuden has either sold complete media or dye to companies such as Fuji, Maxell (Hitachi), Sony, TDK. Unfortunately, those companies also buy from other sources.
For best quality at the highest speed, the DVD drive looks at the brand and other details of the DVD, and checks that against its internal write strategy table. If there's a valid entry, the drive will use that to write to the disc. If there's no entry, it defaults to a standard-low-speed write strategy which should work with all discs. When you buy off-brand or no-brand discs, they will contain strategy information that is "fake" in that it will claim to be, say, a TDK of a certain type. When you use disc ID software, then you believe the manufacturer is trying to mislead you, but in reality the manufacturer is telling the DVD drive what write strategy will give the best results. It's not as important now since the market has matured, but up to a couple of years ago it was useful to keep the drive firmware up to date, since the write strategy tables get added to and revised from time to time.
All things being equal, the best recordable CD should have way longer life than the best recordable DVD because of the dye available to CD. In reality, the recording layer on a CDR is protected only by laquer, whereas on a DVDR it is protected by another 0.6mm layer of polycarbonate.
Some of the "best" DVDRs are no longer made because they weren't profitable.
And all of the above is why I stopped archiving to DVDs and CDs.