The word you use is a map of where you grew up
Very few words in American English sort speakers by geography as cleanly as this one. Ask for a carbonated soft drink and the word you reach for places you within a few hundred miles: soda in the Northeast, around the Great Lakes' eastern edge, in eastern Missouri and along most of the West Coast; pop across the Midwest, the northern plains and the Pacific Northwest; coke throughout the South, where it functions as a generic term regardless of what is actually in the bottle.
That last one is the part outsiders find hardest to believe. In much of the South, a server can ask "what kind of coke do you want?" and be handed an answer like "Dr Pepper" without anyone considering the exchange strange. A trademark has been absorbed into the language as a common noun, the way kleenex, xerox and band-aid were — except that this one stayed regional instead of going national.
Why "coke" happened in the South and nowhere else
Geography again, but of a company rather than a dialect: the drink was invented in Atlanta in 1886 and spread outward from there. It arrived in the South early enough, and dominated thoroughly enough, that it became the default word for the entire category before any competitor could establish a neutral term. Northern cities got their fizzy drinks from a wider range of local bottlers, so no single brand ever captured the noun.
This is a rare case where you can watch a linguistic boundary follow a distribution network. The map of the word is, roughly, the map of an early twentieth-century sales territory.
Where "soda" and "pop" came from
Both are shortenings, and both are older than they look. Soda comes from soda water, the drink of the nineteenth-century pharmacy counter, where carbonated water was mixed with flavored syrup and sold as a mild remedy. Pop is onomatopoeic — the sound of the cork or cap coming off a pressurized bottle — and is attested in British English decades before it settled into the American Midwest.
Neither is a corruption of the other. They are two different features of the same object, chosen by two different regions: one named it after what was in it, the other after the noise it makes.
The one thing to know before voting
Almost nobody switches. Unlike an opinion about punctuation or pizza, this word is acquired in childhood, held unconsciously, and defended with real heat when contradicted — and people who move across the country often keep their original term for decades. That makes this the most reliable match on the site for one specific purpose: not settling an argument, but drawing a map.
If you say something else entirely — tonic in parts of New England, soda pop, or a brand name that is not Coke — pick whichever of the three is closest to what your family says. The interesting result here is not the winner. It is the size of the second place.
Sources: regional distribution of "soda," "pop" and "coke" as documented by American dialect surveys and crowd-sourced mapping projects; etymology of "soda water" and "pop" per standard English etymological dictionaries; founding of the Coca-Cola Company in Atlanta, 1886.