i had the same question two weeks ago. i am using a nec dvd writer. i have found that if i use "DVD-R" i get excellant copies which i can play on both pc and stand alone dvd player, if i use "DVD+R" I also get excellant copies, but.... they will only play on pc not on dvd stand alone player. there are so many variables, disc makers, dvd players ect that i doubt you will get a definitive answer, so i would advise that you buy a couple of each type and try them on both pc and dvd player and see which works best for you. your next question will be what is the best software to use, again no definitve answer depends what you want to copy. hope you find this post helpfull, good luck.
The + system is said to have better error correction and behaves much like a CD-R in use for data.
- has been around longer and has a much better compatibility with DVD players because of this, but most new players will take both to a large degree.
I don't really see one particular format replacing the other, as they look like they can live side-by-side peacefully unlike VHS and Betamax.
The discs you will find best for your recorder depend on your recorder (brand, quality) and recording speed. A cheap brand recorder and cheap brand discs may not be the best solution, whereas best brand/discs is expensive, so best just try and see what works.