I have that reaction to all USian soda (am UKian) because of HFCS rather than straight up sugar. Honestly, to me, the diet stuff actually tastes slightly less awful.
Weirdly, diet Tropical Tango tastes better to me than the sugared version, possibly because its flavourings are so artificial already that the artificial sweetener fits better ... or possibly just because I'm weird.
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
Weirdly, diet Tropical Tango tastes better to me than the sugared version, possibly because its flavourings are so artificial already that the artificial sweetener fits better ... or possibly just because I'm weird.