Real-sugar soda variants in the US (we do have them! And not just imported Mexican coke!) usually come in glass which makes it harder to do a useful side-by-side tasting. I do prefer them, but I'm not sure how much of that's the glass. Meanwhile, I can tell instantly when I've accidentally tasted something with artificial sweetener in it. I've even picked it out from products that have real sugar but are supplemented with a bit of something artificial, waaaaay down the ingredient list, having no idea in advance that it'd be there.

[EDIT] I should add that I'd be surprised if the sugared variants typically have no difference to the HFCS sort other than subbing out the sweetener, so that's another wrinkle to attempting straight comparisons of sugar vs. HFCS