If you are raising a family, Spring Hill has a lot of young couples with children as well. Just north of Spring Hill is Thompson's Station which is all in Williamson County. I believe Thompson Station is unincorporated.
The advantage that Spring Hill has over Nolensville is the access to the interstate,I-65, its proximity to the Franklin and Cool Springs for activities and I believe it is also closer to Nashville than Nolensville by travel time though it probably depends where in Spring Hill or Nolensville you live. Plus, Spring Hill is getting surburban type stores like Target, Lowes, etc .... .
What has happened is home prices in Franklin have shot up and Nissan moving its national HQ has not helped lower them. So, that has pushed up home prices in Spring Hill and Thompson Station. Spring Hill has been approved to have a hospital built there even though one sits a few miles away in Columbia and another one in Franklin. It's a growing area and I don't know if this is true, but someone told me that 5,000 more homes are scheduled to be built in Spring Hill.
Speaking of crime in Williamson County. FYI, Williamson County is one of the top 15 wealthiest counties in the United States
Williamson County, Tennessee - Wikipedia, the free encyclopedia . The crime danger you would face in Spring Hill is probably having eggs thrown at your car after teenagers returning from a Young Republicans meeting see a Hillary for President sign in your yard.

The biggest crime story in Williamson County has been the Sheriff busted for illegally buying prescription drugs. Where did he get busted? In Nashville,Davidson County, of course!
I do NOT mean to downplay the existence of crime as it can happen anywhere. Generally, in the greater Nashville area, you know where not to be in order to be safe(er).