From a hydration point of view, it makes no difference. The dissolved carbon dioxide in sparkling water has no impact on your body's ability to absorb it.
The bubbles themselves might fill up your stomach temporarily and it’s hard to chug a lot of fizzy water at once, but for a given amount of water consumed, you’ll be just as hydrated with or without bubbles.
Fizzy water is slightly acidic, which could theoretically erode your tooth enamel. But the effect is vastly less bad than drinking sugary fizzy drinks or fruit juice.
So, if you choose fizzy water over cola or orange juice, you’ll be improving your dental health.
Other potential effects are more tenuous.
