Be very careful with helmets. Speaking from a motorsport perspective, you need the entire safety package to be compatible before a safety measure is really safe - this includes cabin layout, belts, seats, etc
Even then, and accident is so chaotic that it's difficult to be sure any isolated safety measure will make things better or worse. For instance, the mass of a helmet could kill you through neck injuries or simply because it causes you to hit the panel when you might not have otherwise.
Of course a helmet could also save your life, 100%, but just don't be sure it's a completely clean cut decision.
Generally, a well fitting, extremely light, full-face helmet will be better in most situations (especially if you don't have a full harness). But very few of us are going to fly around looking like the stig! (apologies to the non-Brits who may need to google "the stig"!)