This is the most important about those two formats, I think - competition!
On doom 9 I found one difference one might be judged as a real advantage of DVD-R(W), to quote:
What is the capacity of a DVD disc?
DVD-R/W: 4,707,000,000 Bytes, i.e. 4,489 MB or 4,38 GB
DVD+R/W: 4,700,000,000 Bytes, i.e. 4483 MB.
About 6MB more for DVD- Well not so great.
To quote from Why DVD+ is superior to DVD-, some advantages of DVD+ are
linking: "So the smaller the gap and the jump, the better quality and compatibility we get : -RW allows a 32T large linking gap and does not care about this slicing level jump, while +RW allows a 8T large linking gap and a maximum limit for this jump under any condition."
Multisession: "So every -R(W) recording session has to start with a border-in area (except the first one, which starts with the lead-in) and stop with a border-out area. However, the size of these border zones is quite amazing : 32 to 96 MB for the first zone, then 6 to 18 MB for the next ones. This means that a (DVD-) disc containing 3 recorded sessions can require up to 132 MB (more than 2% of the complete storage capacity) just for separating these regions. ...On the other hand, when multiple recording sessions are used on a DVD+R(W) disc, Intro and Closure zones are used(the counterpart of border-in and border-out), but they are always 2 MB large : therefore, with + format, a 3 sessions disc always uses only 4 MB to delimit the regions"
which is really on DVD+Â´s side.
Then again, read:
"... partially record a DVD-R(W) disc ... border zones are used, which are meant to make this partially recorded disc compatible with standard DVD-ROM players." So the + region delimiting may not play well on std DVD-ROM hardware?
To close, there is one quote which I think tells it all, also from the doom9 FAQ:
"Questions you should not ask
... 2. Is DVD+ or DVD- better? You'll only cause flamewars, fought by users who use single-format writers and who have paid more than they are worth..."