The typical rebate is around 5-10% with auto-rebates (say MGM express comps) and 25-40% with a host (usually for larger comps like room or more)

The "4 hour" thing is only a guideline but you can achieve it anyway you want. "4 hours at $200 average bet" can be 2hr x $400 or 8hr x $100 or any combination.

The best ones are large chains like Caesars Group or MGM group - either chain has tons of casinos, and all the play from any casino count towards your comp.

But baseline - do not EVER gamble for comps.