DVD-R is more compatable with older DVD players but will have less video qualty DVD+R will have more video qualty but be less compatable with older DVD players
Maybe I haven't used them both many times, but I have yet to notice a difference. The -R discs are the ones most DVD players will play. +R are a newer format, which most new DVD players will play. I've always used -R for DVD Video, and +R for data backups, and other stuff.
No, you cant notice the difference I use -r all the time for videos the quality is good. So dont worry about that. Stay with -r they work on 99% of the dvd players. As for +r i say you just use them when you want to burn data disk.