Both of those articles point to the same study.

While that study does raise a good deal of concern about the limited value of diet sodas in weight loss, it does NOT support the claim that they're WORSE than normal, sugar-containing soda as CBear attested.

The inferences made based on that study support the concern that diet sodas are bad for you in glycemic terms (and perhaps behavioral terms as well); on the other hand, the bad glycemic impact of sugar-containing soda is already well-established, and they present no evidence that diet sodas are in any way worse (they don't appear to compare to sugar-containing soda at all.)

The only sugar-vs-fake sugar comparison given in either article is an off-hand reference to a study referring to saccharine in rats, which then links to an article that doesn't mention that study -- not very helpful.