Lot's of things to consider....full face, 3/4, half with detachable part that goes around ears(i.e. h-d Americana style), going to wear face shield, etc.?
What kind of bike do you ride? If Ultra Classic with intercom/CB, are you going to be using it to talk to passenger?
I use the h-d Americana half helmet with detachable part and have a face shield on it. It was only one that fit in shop when I bought bike and other places were about to close. I plan on going to full face for winter riding and may stay with that or add 3/4 helmet. Thing with mine is that when I take off the detachable part, I can slide helmet off without undoing the strap.
Makes me kind of wonder what would happen if I went down on road. 
What kind of bike do you ride? If Ultra Classic with intercom/CB, are you going to be using it to talk to passenger?
I use the h-d Americana half helmet with detachable part and have a face shield on it. It was only one that fit in shop when I bought bike and other places were about to close. I plan on going to full face for winter riding and may stay with that or add 3/4 helmet. Thing with mine is that when I take off the detachable part, I can slide helmet off without undoing the strap.