LNG weighs less than CNG? I did not know this.
LNG is more compact than CNG. It requires less volume to store the same BTU’s.
It also requires refrigeration down to -260°F. That liquid is going to start warming after it is loaded into the vehicle. In a long haul truck or a local fleet service that returns to a service center every night, that is a manageable issue. It would be more difficult for the typical individual commuter.
But the same BTU’s in LNG or CNG will weigh the same. It is the same molecules.