Kate
Okay, I really think that it was wrong the way the producers and Kirk Cameron treated Julie McCullough. There is no excuse to have done what they did to her while she was on the show and even afterwards when they tried to get her back. She deserved better.
Having said that, I must confess that I LOVED the character of Kate and had a HUGE crush on Chelsea Noble at the time. Even now, she still looks great! And I personally believe that Mike and Kate had much better chemistry than Mike and Julie, probably for obvious reasons.