I've played both sites. I have no doubt whatsoever that RHP is the better site. Perhaps I didn't find my way around Chessworld.com as happily as I have with RHP, so can't give a complete judgement.
But one aspect struck me forcefully. On RHP, the ratings of people I know OTB do approximate with RHP ratings, perhaps a little on the high side (and in my case currently, more than a little). But the relativities seem about right, in the main.
On Chessworld.com, you start by declaring your own rating. This is not a bad idea, even accepting that fools will exaggerate. Things will pan out in the end. I recognised one name I knew OTB who was a regular there. He was rated 2050. I'm better than him OTB so I pitched myself at 2100. Within a dozen games or so, I'd soared to 2500, beating plenty of 2400-2600 in the process.
This is great for one's ego, if one is seduced by such nonsense. One might really believe one is a budding GM after all. But then one re-enters the world of grown-ups. What sort of rating system propels me from 2100 to 2500, and sustains me there? Moreover, at 2500, you might suppose by RHP standards that I'd shot to the top of the leader board. No way! I wasn't even in the top 100.
OK, different sites can have different rating systems; what counts is the reliability of the system to reflect relative competence in the game. If 2500 on Chessworld = 2300 on RHP, no great harm is done.
But then I looked further. On the Chessworld.com site, Yelena Dembo (a Greek WGM) is a player. I know Yelena; her OTB rating is 2400+ and her Chessworld rating is 2800+. That seems consistent, up to a point, with my own elevated rating on the site.
So was Yelena top-rated on the site? Not at all. She barely scraped into the top 10
Indeed the top 5 were all rated 3000+, in my view a shameless (& shameful) state of affairs.
So, while I wouldn't want to write off that site, RHP seems better adjusted to the real world. And hence, I continue to play here,but not there