Trump support in a primary may or may not be the decider
Both candidates have run crap campaigns.
The general is going to be tough
The best candidate is not in the run off
I believe Kemp has been the best candidate from the start, broadly experienced with a strong personal presence. I like Hunter Hill a lot, but Hunter lacked the statewide name recognition and support base (outside North Atlanta) that Kemp built as secretary of state. Clay Tippins is a solid conservative and a good guy, but failed to inspire and gain any traction. Casey Cagle is the squirrely hack who endorsed Jeb Bush and stabbed senate social conservatives in the back.
All that said, I don't know how you expect any one of the aforementioned GOP candidates to have a tough time against against the black socialist Stacey Abrams. The gubernatorial race will be decided this Tuesday.