RESs (Resource Extraction Sites) are
only found in planetary rings - they're places where miners gather, and therefore attract a lot of pirates, making them good for bounty hunting.
A Haz(ardous) RES is one that's not policed, so there's only usually ever bad guys and working guys, so there is no law enforcement to either back you up or get in your way.
AFAIK (I'm sure someone will put me right if I'm wrong!), the NPCs in Haz RES instances scale depending on your skill level, so there is no real benefit in scouring the galaxy for one particular high-paying system... it all depends on you, and the bounties that get paid out in that particular system.
You can maximise your payouts by using a Kill Warrant Scanner: This identifies any other out-of-system bounties on a WANTED guy's head, and gives you a significantly better payout when you cash 'em in.
Hope that helps!
[EDIT]Try the latest
Community Goal in Lidpar - you not only get bounty payouts, but also a big fat paycheque when it finishes. Don't forget to register at Carlisle Station first!
Also, I believe one or more of the Powerplay Systems has a bounty bonus...
