Usually. it would be Orange Relentless, or Full-fat Coke/Pepsi - but at the moment I'm on a purge to lose about a stone, and seeing as the sugary drinks are my biggest vice, I've had to switch to a no-sugar alternative.
I detest saccharin and aspartame sweeteners, and the only commonly available 'diet' pop I've found (so far) that contains neither, is diet Vimto.
So, at the moment, It's just that..... and pure fruit juice.