Bartell sounds like a Democrat running on the GOP ticket. Isakson is rather moderate and probably best connected, plus he's from Atlanta. However, he's run before and hasn't done too well. The state has tended more toward the GOP since he last ran though.
Cain and Collins both sound more conservative. Collins gets the edge down here because he's NOT from Atlanta, but then again, Cain gets points for being a successful businessman and not a politician.
I may not get to vote for any of them though; I might have to vote in the Dem primary in order to have a voice in some local issues.