Some notes about my own selections:
If you watch the GRAND clip, that had to be one of the better casts ever on a failed sitcom.
The PHYLLIS theme is almost always mentioned in discussions of the best TV themes ever.
The CLASS OF 65 theme is an extended version of the show's opening theme. They expanded it into a single, much as the FRIENDS theme (which I liked) was extended into a single (which I didn't). I always wished there was an extended version of Kim Carnes' MY SISTER SAM theme, but I've never found one.
Did y'all know that ONE DAY AT A TIME was co-created by actress Whitney Blake and was loosely based on her experiences as a single mom, including with her daughter Meredith Baxter (to this day, it feels wrong not to type Birney)?
And, of course, I'm sure y'all know that HAPPY DAYS came from a LOVE AMERICAN STYLE skit called LOVE AND THE HAPPY DAYS.