We are using the HGU-56. They aren't bad helmet's but I miss some things about the SPH-4B that I used to have. My biggest beefs are: 1. The -56 is it is about as wide as a barn door and catches alot of wind when I stick my head out so that casues alot of wind noise that makes it difficult to hear and 2. The liner has a tendency to bunch up when you put your helmet on causing "hot spots".
There is a workaround for the windnoise; CEP's. They are little earphones that plug into the helmet and double as hearing protection. The "hot spot" problem is a little different. If you are fortunate enough to have a misshapen head, you can get a Zetaliner. It seems to be made of the same stuff that those contour pillows are and conforms to your head every time you put it on. I don't understand why they are not part of the standard issue.
As far standard helmets across the services, I don't think that the Army will be willing to spend the additional money for the helmets the other services are using. Don't get me wrong, the -56 is not substandard, it is just designed with only rotary wing operations in mind.