I've been PHS and GHS both and personally, I prefer GHS...In addition,considering money value, i prefer to stay at the other hotels such as Grand Hilton Seoul or Interconti due to the lower price than GHS and PHS. GHS and GIS has more or less same facilities but CHEAPER THAN both!!!!
Since our branch office is located in Gangnam, I ususally stay at interconti due to price.