Pepsi!
We always had both at home when I was a kid, my dad only liked Coke, and my Mom liked Pepsi. My sister to this day insists they taste exactly the same. I don't know hoiw she can say that. She used to try to trick me and give me two cups with Coke or Pepsi in them and ask me to pick which one was which. She always seemed shocked when I would say, "Why did you give me two Cokes/Pepsi's?" Then she would try both and insist they tasted the same. Pepsi has lemon in it, Coke has orange, that's the main difference.
Her hubby and her used to fight all the time when she would buy whatever was on sale and he didn't like Coke at all and she would get very upset when he would insist he could tell them apart, "Like any sane person could!"
She can't even blame it on drugs..