Some things to keep in mind:
Property Taxes will be cheaper in Williamson County, and crime rates are lower, so you are on the right track. If I could work in Georgetown or Leander, and wanted some land, I might look up around Walberg or Andice or Liberty Hill (all within 15 miles or so, and fairly rural). Not sure if you want land or just a smaller bedroom community. Lots of places popping up about half way in between Gtown and Leander,
Otherwise, I have had family in Leander for over 100 years (HS stadium is named after my Grampa) and Georgetown in the last 20. Either one is a nice place to live within a decent driving distance of just about all you could want to do. I believe RRISD schools are rated slightly better, so I live in Round Rock attendance boundaries, although I chose not to live in the city limits but in the county.
My water bill is hardly ever over $100, but I am in a MUD. I have a sprinkler system that runs twice a week except for Nov - Feb.
I don't think you could go wrong with either. It's about personal preferences. You could explore most of all of this in a day, if you have time to come look.
Class of '93 - proud Dad of a '22 grad and a '26 student!