Saw it in 3D as that was the only option in the time slot we had.
When 3D came out again a few years back I went to see a few 3D films and could never really see much 3D effect going on, so I started avoiding them.
In Star Wars I could actually see the effect in a lot of scenes, but I’m not sure it really added anything and in some cases I think it took me out of the action rather than immersing me in it. Some scenes reminded me of paper cut out animations, or those puppet theatre type things where you create depth by having different layers of scenery behind each other. Certainly doesn’t make anything look more real IMO. Also things at the edges were a bit blurry, although that could just be my fading eyesight I suppose.
So I’d say 2D, but the Cool Uncle point raised above is a good one!