Basically you should be using -R media unless you have a specific DVD player which requires/performs better with +R media (and those would be from specific companies I think, like my girls Sharp progressive scan DVD recorder. Edit: she just told me her Sharp is -R only, not +R)
Check this from wikipedia:
http://en.wikipedia.org/wiki/DVD
The DVD Forum created the official DVD-ROM/R/RW/RAM standards and the DVD+RW Alliance created the DVD+R/RW standards. Since DVD+R/RW discs are not technically DVDs as per the DVD Forum standards, they are not allowed to display the DVD logo. Instead, they display an "RW" logo, even if it is not rewritable, which some consider to be deceptive advertising. However, they are readable by most DVD drives, so they are commonly referred to as DVD+R and DVD+RW.
The "+" (plus) and "-" (minus, dash) are similar technical standards and are partially compatible. As of 2005, both formats are equally popular, with about half of the industry supporting "+", and the other half "-". Around 90% of DVD readers (drives and player) can read the recordable formats, with DVD-R having the best overall compatibility in independent tests. Almost all DVD writers can write both formats and carry both the +RW and DVD-R/RW logos.