@dyslexic: Both are great choices if you're looking for a gaming TV, and feature all the options you'd look for such as Auto Low Latency Mode (ALLM), Variable Refresh Rate (VRR), HDMI 2.1 support and so on.
The only minor difference is the QN90D features Freesync Premium Pro, while the S90D features Freesync Premium, however both models will provide high resolution, high frame rates and low latency for supported consoles and PCs.
