Johnson. Harding also plays 22 minutes a game to Johnson's 17 minutes and Knell's 16 minutes, so his edge in some other raw stats like rebounds isn't as meaningful when controlled for minutes played. In spite of fewer, inconsistent minutes played, Knell has 11 more 3 point makes on the season than Harding (33 to 22), and Johnson is tied with Harding (when you add it today's stats, ESPN hasn't updated it yet).
By the way, a higher FT% is pretty worthless considering Harding has averaged 22 FT attempts on the season, which means he shoots fewer than 1 per game. Maybe if Harding were getting to the line 5 times a game that would be significant, but as of right now, it isn't.
Also, I disagree with Harding's defense or ball handling being better than Johnson. Harding makes fewer mistakes, but that's because he's not making plays either. He doesn't attack the rim or attempt passes in traffic the way Johnson does.