DP is the modern display connector. HDMI is archaic in comparison, and is pushed around only because of HDMI cartel that controls TV business. Basically, all new features in drivers are first supported in DP, and only later added to HDMI. Genreal rule of a thumb - avoid HDMI whenever possible, unless you have no choice but to use it. For sure never buy monitors that are HDMI only.
I would say that this comparison is more convenient if we are considering higher than 1080p resolutions, especially on 4k and higher, adaptive sync technology, such as G-sync, high refresh rates, such as 120 Hz, and multiple displays setup. Other than that, considering the BenQ EW277HDR, I am not aware of any other differences between the current Displayport and Hdmi versions. So not having a Displayport on this particular monitor is not as bad as it sounds. In fact, it's not bad at all. Hope this helps