A:Answer It largely depends on what features you want for the monitor and what you are willing to pay for them.
The tech specs for their panels are about the same, and both have AMD FreeSync. Their stands look different, but the stands have the same ergonomic drawbacks, there is only a tilt adjustment. There is no VESA mount on either monitor, so wall mounts or third-party stands can't be used. Both monitors have one VGA connection and one HDMI connection. Neither monitor includes built-in speakers.
The S2718HN has a narrower bezel. Its HDMI connection is capable of accepting both HDMI 2.0 input and HDMI 1.4 input. It accepts UHD (3840x2160) input, but it is not a UHD monitor with true HDR capability. The S2718HN scales 3840x2160 to 1920x1080 and uses the Dell HDR feature for HDR10 content. The S2718HN includes an audio line-out port to connect speakers.
The SE2717HX's HDMI connection just supports HDMI 1.4 input. It doesn't have an audio line-out port. On the other hand, the SE2717HX is less expensive than the S2718HN.