DVD-R was the first standard for writeable, but then DVD+R came along.
DVD-R tends to have better player compatibility than DVD+R, but using bitsetting, which makes the recorded +R media report it's type as DVD-ROM can help player recognition - in general, if you are recording +R for a standalone player, you SHOULD bitset it to DVD-ROM, if the option is available).
DVD-R media tends to be cheaper than +R, though until recently, there was more junk media in -R, but +R is catching up in that area.
If your drive only supports one standard, then you have to stick with that one - even if you have a dual format drive, they often favour one, in quality, or in getting higher speeds on +R