Both are great anime in my opinion,you picked two amazing ones! InuYasha is a bit longer of a series and considering it also has InuYasha:The Final Act which is ongoing if I recall. The series is funny with a lot of action some good characters and interesting villains as well there are some interesting episodes and fights,Special is a little shorter of a series it had about 20 episodes or so and is one season which most likely would take a shorter time to finish it had amazing characters especially the main characters Hikari-san comes to mind it's really funny too but it mostly takes place in school,Special A was a really fun anime and I think it would be a perfect choice to watch first but in the end it's your choice.

I think everybody should see Inuyasha at least one's

Special A, it has l think, 13 ep. and has a great plot line, cute story. Whereas Inuyasha is a great but, it has filler and drags on for a while, I would recommend reading the manga.