An old laptop dvd-rom (quite difficult & expensive to replace) reads both DVD-R and DVD+R with Booktype set to DVD-ROM. It reads the DVD+Rs much faster! So, if it is not for compatibility with an old device (DVD-Player or whatever), I would recommend DVD+R. I still use both but I have not written so many DVDs so far. As the laptop read DVD+R better, I think about moving there. Price of quality media can be a reason, too.
In "articles" (see top of cdfreaks) you can find a good article to start with containing some technical information (but well and comprehensible written) at http://www.cdfreaks.com/article/113
which may help you to decide. But as everyone here says correctly, compatibility with your other readers will be the main factor in your decision.
If you dont know about compatibility, maybe get a single DVD-R and DVD+R of a quality brand like Verbatim and write them (dont forget to set Booktype for the DVD+R) with a DVD-Video (coz players may not read anything else) and see whether all your devices can read it.
Hope it helps a little bit.