If you want or need the S-Pen, there's nothing to decide, it's the Note line - Note 8 now or Note 9 in September.
As far as specs, the Note 8 screen is larger (6.3" vs 5.8"), the Note 9's rear camera has a slightly faster lens (but still no match for the Pixel's HDR - no other camera is), and the Note 8 has a Snapdragon 835 or Exynos 8895, while the S9 has an Exynos 9810 or Snapdragon 845.
So it really boils down to the pen - the Note 8 has nothing (other than sceen size) that's as good as the S9.