Lots of good options would fit the bill (native Texan, have lived in several places in the state):

D/FW has been covered pretty well, personally I'd go for the Richardson/Plano area (maybe even up to Frisco or even further north toward Little Elm to get a bit more house/$$$). Close proximity to "big city" stuff AND a large lake.

Houston also covered well; the north suburbs are a little less flood prone, but personally I prefer the suburbs closer to the Gulf (Friendswood, Clear Lake, League City, Pearland, Kemah area) for things to do; access to downtown, galleria, medical center from this area takes roughly the same time as access from the north/west areas. Sugarland (SW) is also nice.

However, if natural beauty and outdoor activities are strong needs you should also consider places like San Marcos (one of my favorite areas in the state) and El Paso (Chihuahuan desert splendor + southern Rockies, good crime stats, great food, and close proximity to some of the most desirable areas of NM which offer several ski areas, unique natural wonders, and even better food).