From experience which is the most efficient. I always find the GARCH family models over estimate realized vol. Heres a great website to use for vol models. Also when delta hedging, when we use the close to close model we delta hedge EOD, or EOW whatever your time period is. When we use the Garman Klass model we hedge intraday to capture the log(hi/lo) but what about the GARCH family? When do we hedge to realize GARCH vol?