Never saw Open All Hours, I don't think.
However, I am a HUGE John Travolta fan and have been since I was a little kid. My mom loved him, which made me a fan. We had all his movies on tape, and saw a lot of them at the movie theater when they would come out. So, naturally, when I found out Welcome Back, Kotter had Travolta in it, I wanted to see it. I eventually did see re-runs of the series on TV, and I loved it. I haven't seen an episode in a long time, but maybe I'll get around to buying the DVD set one day, you never know.
But yeah... loved the show because of Travolta, and since it's going against something I had never seen before in Open All Hours... Welcome Back, Kotter easily gets my vote here.