What OS should I use?

I've installed a lot of macOS on my laptop, I feel like I still don't get it what should be the best choice. My goal is to use my low spec pc smooth enough for web surfing and watching YouTube. I'm making a choice just between Catalina and Big Sur. I think after using Big Sur for a day, it was too much. Little laggy. What should be the better choice for me? Another question is, every time I upgrade the OS, is it getting harder for low spec pc to make a better performance?