The Exynos-powered models from previous Galaxy S models appeared to be slightly faster than the Snapdragon versions, but it looks like the situation is now reversed for the upcoming Galaxy S10 handhelds. Early samples of the Exynos 9820 and Snapdragon 855 tested in AnTuTu show a slight advantage for Qualcomm's chip, but the final versions might provide different results.
https://www.notebookcheck.net/Snapdragon-855-beats-Samsung-s-Exynos-9820-in-latest-AnTuTu-benchmarks.374621.0.html