I'll sometimes accidentally use 'Coke' as a universal term for sodas, so I guess I'll go with that.
I probably wouldn't be able to taste the difference between the two, though.
I actually like coke and pepsi pretty much equally.
If it was a choice between pepsi or vanilla coke, on the other hand, vanilla coke would win hands down.
To be honest, I choose either one depending on what's available and my mood at the time. That being said, if it was a choice between Pepsi Max or Coke Zero, I would have to go with the former, as I find the latter tastes horrible.