I would say there is no clear answer to that question.
While 2) and 3) can easily be ruled out, plasmids (mostly circular pieces of DNA) are a very convenient way to transfer recombinant DNA into bacteria and also small eucaryotes like yeast, and these are the most commonly used organisms in current research.
Genetically manipulated viruses are mostly used in animals or plants, since in these organisms, the use of plasmids is not suitable.
So it depends on what organism you talk about. If i had to choose, I would say 4), plasmids.

4. Plasmids

Viral vectors can be used, but transfection with plasmids is the most common method. Often in laboratories, plasmid vectors will be used prior to viral vectors, for example a plasmid with antibiotic resistance will be transformed into one bacterial strain and then a viral vector (phage) will be used to transfer it into a different strain.