An HMD is a Head Mounted Display.
We call them “headsets”. The part of the VR equipment that we put in front of the users eyes. They include lenses, screens, and straps, bands, or another means of keeping the thing attached.
Headsets often also include speakers and some amount of tracking technology.
If we talk about headsets that are “better” we are probably speaking in one of two contexts: quality and comfort.
Quality meaning how good the technology inside of them is, attributes such as tracking fidelity, screen resolution, latency, visual distortion, and so on.
Comfort meaning, basically, everything else: comfort and ease of use: weight, ease of cleaning, how annoying is the strap is, how likely is ones hair to get tangled, if they start to hurt after long sessions, how well the weight is distributed, do the lenses fog up, and so on.