There's little to choose beteen the + and - standards right now. Technically they're very close to each other which is why it's proved economical for manufacturers to produce drives that support both formats.
I tend to choose which standard to use based purely on cost of the media right now. If you're putting films onto DVD then the other thing to consider is which standards your DVD player, or that of others you may share with, supports. Again most current DVD players support both anyway these days.
With new DVD technologies such as Blu-Ray and HD-DVD coming along offering 25-50GB or storage, I don't think we're going to have to worry too much about who may win the + and - war as they're both likely to be obsolete in a few years.
Read more here or just search for 'DVD formats explained' from a search engine for;