-Rs are the only DVDR sanctioned by the DVD commitee or whatever you call them. DVD-Rs seem to play in more machines also but with newer devices, they both seem to work equally well.
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Just 2 competing formats. They both work equally well. -R may be slightly (5%) more compatible since it is a year older. If you're just burning data then it isn't much different than burning a CD-R (except for 7 times more space). I would be more concerned about the quality of the discs rather than the format. Use discs made in Japan if you can find any.
+R's seem to be much more reliable and problem-free in my personal experience and in the experience of half a dozen or so of my professional IT colleagues. Deep in the gory details (see Lkdog's links), the +R's have some technical superiority over the older and more "official" -R's. Most all units these days, both computer and consumer audio/video will read either equally well. I moved from -R's to +R's early on (2+ years ago), and my professional colleagues at work have done the same (both for data and video) - we've simply found them more reliable and trouble-free.