The funny thing is that i have only been to 3 sf parks, 2 of them are no longer (SFWoA and Astroworld). I have been to both companies flagship parks. And one park that was controlled by both companies (Geauga Lake). It is hard to judge a company from their past experiences. Plus I am tainted being from Cleveland, OH. When you have Cedar Point in your backyard, kinda tough not being biased.
I see good stuff happening by both companies. I hope SF operations have gotten better since my last visit to SFMM 6 years ago. Truthfully, I need to do a coaster trip next year to give my opinion. But right now, I lean Cedar Fair.