
I've been a subscriber to Popular Science, Discover, Astronomy, Sky & Telescope and Scientific American for years now.
I'm also an on again, off again reader of scientific books. Primarily on Astronomy, Cosmology, Physics, Anthropology and Evolution.
Of the three magazines I tend to like Discover the best. Astronomy is a little to narrow and covers a lot of observational astronomy which sadly I have little time for anymore and covers too little of the "big pictures".
Scientific American is a close second but often the articles can be either too few or just too in-depth for what a general reader would care about (along with assuming you know what they are talking about rather than being longer, to help better explain to a layreader)
Popular Science should be called "popular technology" not popular science and so I think misses the mark (although it is an interesting magazine) and has WAY too many adverts.
If you can pick only one pick Discover. Get more detail about Discover (1-year).