I've often had exactly the inverse experience on trips to northern CA: so many places, I ask for a Coke, and get told that they only have Pepsi. Mind you, in UK pubs these days, if you ask for a Coke, you'll probably get flat Pepsi out of a hose dispenser - flat on account of the violence of its expression.

I'm not a fan of Pepsi at all, in a similar way to how I don't like any of the diet colas - the sweetness is too much, and it being flat only hurts it further, removing some of the carbonic acid.