The Star Alliance lounge is superior. The QF First lounge at LAX is a big disappointment IMHO. Certainly compared to MEL and SYD.

Diners Club? Seriously? LoL... It's been years since I've been anywhere that accepts Diners without tacking on extra fees. Heck, I've even lived in Chicago where Diners was invented and nobody accepted it there. Citi Prestige is the way to go particularly if you can get the U.S. version. 

Have not been at all impressed. I fly PER-IAH and frankly with poor lounges and absurd flight times it's easier to fly other airlines. EK J Class is horribly overrated IMHO. Chauffer Drive service is patchy.