In my own opinion, if someone has never used pytorch before, they might prefer your version potentially. For anyone who has used at least one pytorch module using the second syntax, the second syntax might look more natural, familiar and compact. At least, for me, the second form looks natural and standard, whereas the first form makes me scratch my head and wonder what is .add_module, and wonder what is the difference compared to the second form 
I assume they will both work identically, from a functional point of view (an assumption though, not having ever seen/used the first form).