It really doesn't matter which you use. I use +R mostly now.
-R is more suited to video/movie use, +R is better for fast file access and backing up 1000's of files etc.
But it really doesn't matter unless the customer has a really old DVD player that does not support the later +R format.
More importantly it is the dye used in manufacture. Get good quality discs like Verbatim etc which are 100% error free.
