I enjoy the taste of diet pop, but I also find myself reaching for it sometimes out of sheer boredom rather than thirst. If I drink some water and I find it bland, to me that's a sign I wasn't actually thirsty.
I don't think there's anything unusual about reaching for a soda as a treat for its taste. But in terms of pure thirst-quenching - damn does water hit the spot.
But there's also genetics. Some people spit out stuff like "omg, that's too sweet! yuck!" I eat a pretty spare diet these days and try to eliminate sugars and other additives, and still, sweet is good. I cannot put together this concept, "too" sweet. My sister doesn't like the taste of red meat, never has. People are just different!
Short of overhydration, there are no downsides to pretty much constantly consuming non-caloric liquids.
It's also what you're used to. There was a time when I would drink a lot of soda, but then I made an effort to switch to just water (and coffee). I almost never crave soda now.
Dressing up water with lemons or whatever takes time. Grabbing a soda from the fridge is dang near effortless.
Plus caffeine.
Acid + teeth is not a good mix.
It's not much of a decision point, I don't really think about it in terms of expected value or return on my choice, diet soda is simply the answer to the question of, "What are you drinking?"
And despite articles like the submission, there's no real observed downside to this choice (I'm not obese, and have never been obese, so this article doesn't really apply to me), other than potentially what the carbonation could be doing to my teeth, and as long as my dentist doesn't seem to have any concerns (she doesn't), I persist.