My heads are built on a baseball cap. Being built on a baseball cap means they are easily adjustable not only to head size but where they sit on your head allowing you place the face lower or higher based on your comfort and range of vision. You can also easily adjust the fit with a bit of foam, in the case of the image above I needed that little sliver of green foamie sheet to make the jaw sit right since it was a tad too tight, amazing how such a thin little thing made the fit go from "meh" to "perfect" Now if the jaw were too loose I would have put the foamie on the back of the jaw not in the brow.
The jaw is hinged via tube and rod and works by bumping your chin. The movement is flawless for silent movement but does voice sync decently as your chin moves when you talk.
The head above has no fan but when I add one it goes in the muzzle where that little triangle of firm foam is (helps keep the soft foam of the muzzle in in its proper shape) I opt to have the fan blow in vs out, I create a deflector in front of your nose to keep it from blowing in your eyes/on your nose (as it can be uncomfortable) and to direct the air across your cheeks, ears and around your neck (I have found cooling the ears and neck helps a ton!)
The only parts that actually touch you are the back of the jaw, the hat and sometimes part of the neck. Your nose, most if not all of your neck, cheeks and ears are left untouched allowing airflow, minimizing the amount of sweat that gets soaked into the head, and creates a less claustrophobic feel (honestly I cannot stand a head made on a balaclava, it triggers my claustrophobia to have my head squeezed and I have to take it off)
The one disadvantage to my method is making the inside look clean, with a balaclava head the inside is instantly lined, but with my method I have exposed foam to cover up and it can look a bit rough. I like to make the whole inside black so there is no exposed foam distracting your vision from the inside, I then sign and date the piece decorating the inside and adding a character name if I am given one.
The neck opens in the back and you simply slide your face in and fasten the velcro strap, which also allows one with glasses to get the head on without messing up their specs (I myself do wear glasses by the way) The neck closes via strong rare earth magnets an thus practically closes itself.
The neck connects from the ears back and the front of the neck gets pulled under your chin, this allows one to "pop the top" as in lift the face up like a welding helmet (the neck stays in place) allowing you to take a quick breather or browse a vendor table without fully de-heading, you can even set the inside of the face on top of your head to be hands free if need be. Now if a kid rounds the corner while your top is popped it is super easy to slide it back down. This disconnected neck is not visible when worn at all as the rim is well covered by the overlapping cheeks and chin of the fursuit's face. *due to the way I build heads I do not offer form fitted necks and a longer fur in the neck area is much advised.
With realistic eyes I like to do huge mesh tearducts that go both at the corner of the eye and under the eye, normally working in the mesh as a black marking around the eye, this allows excellent forward and peripheral vision with minimal blind spots. You can also glance down through the mouth to manage stairs and not tripping over small children.