Regular soda.
I've had quite a few times where someone was like "you should try this diet [name of soda], it honestly tastes like the regular kind!" And yet every single time I tried them...yeah, they tasted nasty to me compared to regular sodas.
I'd rather drink no soda at all than try and drink diet soda, even if I'm really craving a soda. That's how much I dislike it.