It depends on the player really. Some standalone players don't care much about the book type of the disc used. For those players, they recognise the discs whether you book type them to DVD-ROM or not. In that case, it doesn't matter whether you use +R or -R. If you have one of those standalones that only recognises discs booktyped as DVD-ROM though, you might do well to go with +Rs.
I suspect that in the end, it will really depend on which ever type of media is cheaper for you where you live.