Entirely dependant upon your usage.
In terms of screen 'quality' the S8 Ultra is superior due to the S-AMOLED display vs IPS, its also better for media consumption due to the aspect ratio and its much larger 15.6" screen vs 12.9".
The iPad's m2 CPU is much more powerful though and the battery life is superior but I find editing and viewing photo's a much more pleasing experience on the S8 Ultra however the thing that killed the iPad for me was how iOS managed its file system. I hated it and as windows / android user it feels like having your hands tied behind your back.