Nashville, specifically Williamson County just south of downtown... Brentwood, Franklin, Leapers Fork, etc.
Good economy. Growing city. Consistently rated among the top destination cities in the US. Low cost of living. No state income tax. Great schools in Williamson County.
Friendly people. Most have relocated to Nashville for job opportunities and stayed. Lots of food choices. Lots of outdoor cafes. Lots of greenways to run. Active running club for recreational runners... not much if you're into adult track. Lots of hills for running at Percy Warner Park. The Nashville Half and Marathon typically draw 34,000 participants.
Good weather. It really doesn't get that cold... 20s for a few days, but if you can run later in the day, a typical January high is maybe 40 degrees. It snows enough to cover the roads maybe two days each winter. Summers vary, but it didn't get over 97 this past summer.
Blue Ridge mountains are 3 hours. Pensacola Beach is 7 hours.
My biggest running peeve is that the dirt trails around Nashville are all technical single track.