I switched from S9 to Xs. I'm happy I did, but it's a very subjective thing. The question is not whether the Xs is better or worse than the S9, but rather whether iOS suits you better than Android or not. And only you can answer that.
Both are state of the art devices in their own worlds. The Xs is the best iPhone of the day, while the S9 is (or was, until very recently) the best Android phone on the market. You can't go wrong with either of them.