Nashville vs Phoenix for appreciation

[Crystal H.]

I live in the Nashville area and have a friend looking to escape San Francisco so their family can purchase their first home (cost prohibitive to do so in SFO) 

Their options are Nashville area (south of town, need good schools so Williamson County) and the Phoenix area (also near good schools, I'm less familiar with this metro). Their plan is to stay a few years, rent a couple of years (likely move to Europe to be closer to family) and then sell while they can still get the tax advantages. 

Has anyone looked at these two markets head to head?