Most modern DVD players will play both + and - formats. If your player is older you may find it only plays - format disks.
Use the minus disks because, at the present time, they are cheaper.
We get out disks from click here and click here
Be careful to buy disks suitable for your burner as most burners can be faddy as to what they burn to.
Both of those companies, above, do selection packs of disks if you can't find any specifically recommended for your burner.