Depends if you mean to backup a DL movie to a DL disc or SL disc.
If no compression or stripping out extras is required then DVD Decrypter using ISO read mode - possibly in conjunction with AnyDVD for removal of the latest protections - would be best. Then burn with Decrypter or Imgburn.
If burning to SL discs then CloneDVD or DVD Shrink (both with AnyDVD potentially) to an ISO image & burn with ImgBurn is the way to go.