Hi Peter,
>>>>>Does anybody know what will be better to use as Save as file format in DWG.....2013 or 2018 ?
If you (and people you share your drawings with) are using AutoCAD versions which supports 2018 DWG format, then it is better to use 2018 format. It includes optimizations to support new features introduced in 2018 and later AutoCAD versions. In addition, the 2018 format fixes some bugs of the previous format, for example: a bug when the attributes containing multiline text could change their location in the block each time the file is saved (in 2013 and earlier DWG formats) - now, when saving a drawing in 2018 DWG format, this bug will not appear.
On the other hand, if you share your drawings with lots of people, or you have a wide variety of AutoCAD versions in use, e.g. 2015, 2016, 2017, 2018 etc. or you have a large archive of older drawings that you need to keep in their current 2013 file format, then you may consider to use 2013 DWG format.
>>>What are the differences ? And what are the benefits ?
DWG file format which is used in Autodesk products is a proprietary binary file format. "Proprietary" means that this "file format is format of a company, organization, or individual that contains data that is ordered and stored according to a particular encoding-scheme, designed by the company or organization to be secret, such that the decoding and interpretation of this stored data is easily accomplished only with particular software or hardware that the company itself has developed. The specification of the data encoding format is not released, or underlies non-disclosure agreements." So nobody can tell you exactly about the differences.
