Seymour. Your practically in the middle of the other two. I live in seymour, and I've been pleased for the last 6 years. Plus, Seymour is in both blount and sevier county, and maybe even knox. But you get the touristy type tax breaks from sevier county without living amongst them!
I have lived in Powell my entire life and wouldn't want to live any closer to down town although it is slowly moving this way! Halls,Powell or Karns would be my choice. It really depends on where you are working as far as the 30 minute commute.
Where will you be working?
I grew up in Karns/Hardin valley and loved it. Not to far of a drive from work and hunting areas. I just recently moved to rockford, right between south knox and alcoa, but will be moving back at some point due to i work in oak ridge