What is / was your favourite pop to use for these, when I was a kid they had to be made with cream soda, I bought a bottle of cream soda earlier and that is what reminded me, now which freezer is the ice cream in?
It's about half a century since I last made one but my automatic choice would definitely be cream soda. However this might be of interest if you're thinking of experimenting with something else: https://en.wikipedia.org/wiki/Ice_cream_soda