Certain blank DVDs are in the + format, others in the - format. This difference isn't exactly important nowadays however, since most drives that come out nowadays/come with computers can burn on them both.
In the past most standalone DVD player had better chances of recognizing a DVD+R disc than a DVD-R disc. Nowadays I believe both are recognized without issues unless it is really from a cheap no name brand company.
The best advice I can give is whichever media you use, you burn at the slowest speed allowed or 2.4x speed. Burning at high speeds tends to create errors that standalone DVD players cannot read. The faster the burn speed, the more errors and the greater the chances the DVD player will stop playing the movie or skip to the next chapter (sometimes to the beginning of the movie).
PC DVD drives are better at playing back DVDs with burn errors than a standalone DVD player. However, I would recommend burning at less the rated speed of the disc; typically half of the rated speed, if you are burning DVDs to be read by a PC DVD drive.