Membership yes - ownership now limited to a couple base weeks
The Marriott, Hyatt, Starwood or Westin timeshares offer better amenities in some cases - all the fixings of an upscale hotel - but large rooms like a nicely appointed timeshare. That's why people love them so much. Room service, cleaning, tons of pools, restaurants or clubs onsite - even casinos in some cases.
But as far as how do they compare to the high end - Gold Crown resorts (name or non-name) in RCI? They tend to be more generic and perhaps even a step downward in many cases - a few, and we're talking only a handful of truly special locations - may be better than the "standard" Gold Crown level if there is such a beast.
Overall both groups have some outstanding resorts, many middle of the road and some truly bad locations. II, if there is a pattern to it all, tends to have some REALLY nice resorts but, as mentioned in a prior post, unless you already own a brand name & higher end location of that brand it is highly unlikely you'd ever get a trade in to one of those except seriously off season times. II also tends to have far too many lesser resorts - basically mostly off season times at all resorts - with not as many in the middle range. RCI also has some top line resorts but seems to give all trades access - after their own rentals, of course! But if it slips by renting into the exchange pool you get a fair shot at it. Also they have far more "middle" type locations, not as many hotel conversions it seems and they regularly offer (much to the chagrin of many owners) deeply discounted rentals to even some very good resorts & use times.
Overall we've found exchanging to either group has become far too costly. It is what our annual fees USED to be not that long ago to get a trade. We now feel the value is in renting without actually trading so we reduced our holdings to two favorites under owner control (down from 8+ week in the past) and rent whatever we used to try to get through trade. It works much better as you have far more control over what/when you get and the cost is far lower than owning, paying annual fee, II/RCI memberships & the cost of exchange fees. Get a week or two as your way into the exchange services & then just work the extremely valuable rental offers is my advice.