My coffee tastes extra special when I'm drinking it from one of my favourite cups, so I gotta agree with you here.
Somehow, I cannot drink black coffee straight from an aluminium flask. The taste is just not the same. It could be psychological, which I understand because I do eat with all my senses. Coffee is not so appealing in a metal container to me.
Like my Stanley flask here:
It's insulated and keeps coffee hot for several hours, it is pleasant to hold because the insulation prevents the exterior from feeling hot. However, I have to have a cup to pour it in. 😅