If you have to watch only one GITS series, watch Stand Alone Complex.

If you mean the American movie, no. It's trash. The 1995 anime, definitely watch.

I can also recommend the manga, the first vol. It's packed with interesting ideas and author footnotes that the 1995 hints at but has no time to elaborate on.

E.g. In the movie the protagonist glances an office worker that looks like her. The manga has her explain that she looks like a cheap generic model to hide the fact she is full of expensive specialized government tech. I always think of that scene when I put an expensive work laptop in a ratty backpack.

You should definitely watch SAC and both GitS anime movies, but you don't need to watch them before the new anime.

The new anime is a more faithful retelling of the manga from the start so you can watch it by itself.