Harrington. Not only is Cotton exceptionally bad, I’m inclined to vote third candidate in contests where no Democrat is running. We get some races like that in South Dakota. I voted Libertarian, the only non-Republican option, in the most recent House race, even though Dusty Johnson seems like one of the less horrible Republicans.
It seems like Arkansas Democratic voters did the same as you. Harrington effectively took the place of Generic D, and the results in Arkansas' Senate election display that. He won Pulaski County and the majority-black counties along the Mississippi River; Cotton won everything else. Harrington also came close to winning Washington County, losing it by about the same margin as Biden did.