Right now, "Ooo, shiny!"
Actually, I did pick up the US Mint's medal honoring both the Apollo XI mission and John Glenn, and I'll be getting the ones they issued in honor of Arnold Palmer, Jack Nicklaus and Byron Nelson. The local science museum has three, all of which I've picked up. And there's a Yuri Gagarin medal I picked up that includes metal from Vostok-1, as well as a diminutive Franklin Mint issue that includes metal from one of the Apollo missions -- by includes, I mean they put some in the melt, not that there's a specific embedded chunk.
So, space, science, and golf. There's a combination. Although I know ultimately my criterion is "Ooo, shiny!"