Tough call. The recent Arise series of 4 episodes gives context to section 9, which none of the others do. So watch that first if you want to find out how they came about.
Personally though, I would recommend the original movie, then Stand Alone Complex 1st Gig, then 2nd Gig, then Arise. Then watch everything else if you've still got the motivation to. The second film isn't quite representative of what's great about GITS, and feels more like an indulgence of the director.
See if i couldnt work out the best order to watch them in so i havent as i dont wanna ruin the story