Shiner is about two hours east of San Antonio. I haven't been there. I hear it's nice. It's sort of near Luling, which is a great spot for barbecue.
I love the town square of La Grange, and there is a great meat market, Prause's, there. I found the people really charming there. Very Texas small town.
Don't really know San Marcos, other than it's a university town.