Dvd-rw vs dvd+rw

Could somebody explain the differances between DVD-RW and DVD+RW. Also as a newbe to dvd how do I know when to use one vs the other. I have found this to be very confusing at one time + was double capactity now I have no clue.

http://www.build-your-own-computer-tips.com/dvd-drive-differences.html
http://www.gen-x-pc.com/dvd_vdvr_vdvrw_info.htm

I thank you. It now makes more sense.