There is no quality difference that I know of. At least nothing noticeable to my eye.
A not to you: I noticed that in a few of your threads you ask a question, get a response or two, then re-ask the question with more specifics (this thread and your recent mouse thread). Why don't you just ask what you want to know and cut out the general questions? Example. "Is there any difference between DVD-R and DVD+R? I'm specifically wondering about quality." You'd get better responses this way.