Howdy. I actually live in New Braunfels. I love this town. Just moved here about two years ago, but used to come here to float the river once a year for a few years prior. From what I understand, the schools are great, I know the people are pretty great, and there is tons to do whether you are an indoor or outdoor person. It is growing, but it is still very quaint, small town-ish. The real estate market is very diverse here. There are your typical subdivisions, historic homes, subdivisions with 2.5 to 10 acre lots, homes right in the middle of town and homes farther out.
I know Canyon Lake is moving up in the world, since they just got a new high school. There are some small towns around it that are okay, too. On the edge of Hill Country, you have tons of options.
San Marcos is a nice town, also, but is very much a college town. It is the closest of the 3 you named to Austin. (NB is about an hour and Canyon Lake would be just about the same, I think.) San Marcos is really only about 20 minutes north of NB, so I guess it would still be about a 40 min. drive.
Not sure what else you'd like to know, but I will help ya with whatever I can.