When purchasing an insulated jacket for backpacking, should you buy one with a hood or without?
I think it really depends on how you plan to use it with the other clothing you carry. In three-season weather, I bring a hoodless insulated jacket on all of my trips which layers easily under a hooded rain jacket when I am active and hiking. The nice thing about a hoodless jacket is that the hood doesn’t bunch up under a rain jacket so you look and feel like a hunchback. If my head is cold I simply put on a fleece beanie.
In cooler weather like early spring or autumn, I’ll bring an insulated jacket with a hood since I always use it as an outer insulation layer when I’m not active, either resting or in camp.
In addition to insulating your head, a hood insulates your neck, something that most hats don’t do, unless you wear a balaclava. The downside of a hood is that it can restrict movement, block out sound and your peripheral vision, but these things are less important when you’re inactive.
Perhaps a clearer way to state the difference is that a hoodless jacket is more like a mid-layer that you’d wear when hiking and that a hooded one is more like an outer layer for when you’re not moving. They have different functions although they have many similar attributes.