Which combination of Bradley sisters was the best?

In most cases, the original is best. In my opinion, there is no exception here. I think the original set was best: Jeannine Riley as Billie Jo, Pat Woodell as Bobbie Jo, and Linda Henning as Betty Jo.

I think the original combination captured the girls' personalities the best, as they were supposed to be. Jeannie's Billie Jo was the boy-crazy, ditzy older sister. Pat's Bobbie Jo was the studious, serious, and intellectual sister. Linda's Betty Jo was the fun-loving tom-boy. This was just how the girls were written to be, and they were perfectly cast. It wasn't until just a few years ago that I even knew about the first two seasons of Petticoat Junction. When I saw them, I was like, "wow, this original cast was awesome!".

Betty Jo remained constant throughout the series, and I am thankful for that. Betty Jo would have been the toughest to replace. Nobody else could have captured her character the way Linda Henning did. Pat Woodell and Lori Saunders are actually pretty close. They looked enough alike to make the switch believable. I very much liked Lori as Bobbie Jo, almost as good as I did Pat. Pat was a bit better for the role, in my opinion. She did the studious, intellectual thing better. However, a lot of that may be the fault of the writers. Later on, the writers made Bobbie Jo more silly and ditsy, and Lori played the part that was written. I preferred the Bobbie Jo character to be studious and serious and not the dingbat that she later became.

The two Bobbie Jos were neck-in-neck with Pat winning by a slight margin. However, it's the different Billie Jos that really drives me crazy. Jeannine Riley played the part to perfection. She was silly and boy-crazy and uninterested in academics and only into her social life, etc. However, Jeannine also managed to display a certain sense of maturity as well. She displayed a good combination of being scatterbrained and mature at the same time if that makes sense. I hate that Jeannine left. Gunilla Hutton was a pretty good replacement though. She played Billie Jo pretty close to the way Jeannine played her, and the character remained somewhat constant. Gunilla missed so many episodes too. Meredith MacRae, in my opinion, was awful as Billie Jo. She was the worst. She totally changed the character of Billie Jo. Suddenly, Billie Jo was a career woman and serious and too sophisticated. Also, Meredith had no country attributes. She did not come across as a girl who was raised in the country and grew up at the Shady Rest.