Quite a bit of caving doesn't require much head protection: its just a case of protection from banging your head on the roof and somewhere to mount your light.
Quite a bit of caving requires maximum protection: fall protection, stone fall from great heights, as well as the above self inflicted bangs on the roof.
The trick is to not get the two situations confused! Given that many caves have both environments I wear maximum protection at all times, but really you could make an informed choice to compromise if your caving only takes place in the horizontal.
Comfort is pretty important too. My WW paddle helmet is a Ellios from climbing/caving because I can't find a comfortable paddle specific helmet. I often use a cycle helmet for rock-hopping when sea kayaking. Both are probably being used outwith their test standards but it seems reasonable to me given the comparative useage.