"Pop", of course. Though living on the East Coast when I order pop I usually ask people "What soft drinks do you have?" That way I don't need to say the accursed "soda" but people don't give me weird looks. Like, in Minnesota, if you order a "soda", people will know what you're talking about. In Maryland, if you order a "pop", people will look at you like an alien.
Why don't you just call it by the brand? Can I have a coke? Can I have fanta? etc
It's more like if you're asking for a drink in general...
"Would you like something to drink?"
"sure."
"What would you like? I have pop, coffee, tea, juice"
"what kind of pop?"
"Coke, sprite" etc
You get it.
I've had people stubbornly refuse to believe that people have a generic word for pop no matter how much confusion I show. I've basically word for word given them that dialogue, and they just go, "That never happens, you just say something like 'what do you have to drink?'" and I don't even know how to respond. THERE'S A GENERIC TERM, GOSH DARN IT, FOR FIZZY CARBONATED BEVERAGES. I KNOW YOU HAVE IT SOMEWHERE. REVEAL TO ME YOUR SECRETS.