is not the issue when comparing these cameras - they will be close. The issue is an external mic-in jack. HV20 has it - HC5 does not (though it does have the Sony proprietary active interface shoe)... and the viability of that Sony proprietary "active interface" adapter is a question - plus if it is used, there is no camera mount without getting a camera bracket...

If you know you will be shooting in lowlight, then don't buy either of them. If hidef is a requirement, turn on a light.