I'm more of a contralto kind of guy, tbh.
One of the reason I like Whitney is that she had a deep voice, and she knew how to project, and most importantly, when to project. She could hit high notes, but she also knew when to use them. It is not only about hitting the notes, otherwise you'd be all staning Georgia Brown, it is about having the musicality to know how to use them to add emotion to the performance.
Xtina is one that clearly overdoes that. That girl, besides having a beautiful voice, does the same. It is nice, but it is also tiring. Honestly. No shade.
Edit: for full disclosure, no one is immune to oversinging, and Whitney herself has done that quite a few times, but overall she nailed most performances.