I got my copy of Sterman from my sister (who had studied systems engineering at MIT and so had a copy from her coursework there), but at your recommendation from a few years ago.

I worked through (most of) Morecroft because it was available through O'Reilly's online library and I had a subscription through work. I read Meadows specifically because of the leverage points essay, and wanted to see what else she had. It's definitely shallower than the others, but I think a good introduction because of its relative brevity.