GA-Sen IMO, I think people forget the nature of off years and how both PA and GA voted notably to the right of the nation.
It'll be interesting to see if Democrat's strong ground game in GA continues and how much canidate quality ends up mattering in both races.
GA has the benefit of having an incumbent and an electorate that is largely unaffected by the national environment. Deal was one of the few Republican governors to do worse in 2014 than in 2010 despite being uncontroversial his whole tenure.