Of course always a medium temperature (for me about 20'ish, non-humid) is the preferred one but if it comes down to choosing either sizzling heat or freezing cold no doubt I would take the freezing cold any time. I remember even when I was young back home (where the temperature is 30's, though humid and sweat-inducing) I always hated heat and I remember walking right next to walls and buildings for shade when going to and from school.
In winter (apart from the depressing mood) you can wear jackets and appropriate clothing and catch up some great sleep moments but in the heat I hate everything and everyone. It makes me like sick, easily irritated & lose my appetite. And talking about weather, we've just begun summer and I already hate it.