Since many users ask this question I decided to give a brief explanation here.

There is no difference between the two types that user can see. If you burner supports both, you can try to burn the same movie in both types and see that there is absolutely no difference. So if we exclude the people that have an older techology burner that supports only DVD-R or DVD+R we come to the selection of the media.

The winner seems to be DVD-R as it is cheaper and more compatible with standalone DVD players. research has found that 97% of the standalone players play DVD-R, 75% of them plays DVD+R while around 70% plays both.

The choice is yours!