Which duplicate files should I delete
If a disk drive is scanned for duplicate a very large number will be found - but many need to be retained, and others could be deleted.
A significant number of duplicate files are probably best described as system files. Many names will not make much sense, and unless very knowlegable, it is best not to touch these files.
User files are one that are of most interest, and also having a fairly free form on where such files are stored, can mean that a significant number may be placed in multiple directories. A good starting point may be videos, user shot or downloaded. These tend to be large making savings significant. By searching multiple drives, you can determine if important videos are backed up on different drives. However, if you see below, DVD vidoes have a problem in that many files names are the same - so testing with content is a sensible suggestion.
Some types of files will have the same name. A good example is a video file - maybe from a download or a DVD. These all have files such as VTS_02_0.IFO. For these files, the directory name is important, rater than the exact name, so any type of automatic deletion would be very dangerous.
