There are a slightly different No of secotrs on +R to -R discs, but the biggest "main" thing that the y come about form is which "technical group" support each format and therefore claim "theirs" is best
Recordable formats, supported by the DVD Forum
DVD-R for Authoring: a special-purpose DVD-R used to record DVD masters, which can then be duplicated to pressed DVDs by a duplication plant. They require a special DVD-R recorder, and are not often used nowadays since many duplicators can now accept ordinary DVD-R masters.
DVD-R (strictly DVD-R for General): can record up to 4.7 GB in a similar fashion to a CD-R disc. Once recorded and finalized it can be played by most DVD-ROM players.
DVD-RW: can record up to 4.7 GB in a similar fashion to a CD-RW disc.
DVD-R DL: a derivative of DVD-R that uses double-layer recordable discs to store up to 8.5 GB of data.
DVD-RAM (current specification is version 2.1): 2.6 GB, 4.7 GB or 9.4 GB (double-sided) discs compatible with only a small proportion of other-format DVD drives. DVD-RAM discs were originally typically housed in a cartridge, though these are now less commonly required. Discs can be removed from their caddy and used in compatible standard-tray drives. Rewritable many more times than other rewritable formats.
DVD-AR: Recordable version of DVD-Audio
Recordable formats, supported by the DVD+RW Alliance
DVD+R: can record up to 4.7 GB single-layered/single-sided DVD+R disc, at up to 16x speed. Like DVD-R you can record only once.
DVD+RW: can record up to 4.7 GB at up to 16x speed. Since it is rewritable it can be overwritten several times. It does not need special "pre-pits" or finalization to be played in a DVD player.
DVD+R DL: a derivate of DVD+R that uses dual-layer recordable discs to store up to 8.5 GB of data.