I have high value traders in both (east coast summer beach weeks). I find much more in RCI. I use II to get Marriotts--but I am behind the line for those with M preference. I got 1st week Jan in Aruba at Marriott Surf Club, but only a studio---fine as it is DH and I going, but I had to give up a 2 BR. Otherwise, there was really nothing I wanted at all--but we need to travel with kids at prime times. IIs European coverage is terrible for prime times.
RCI--early bird get the worm--I got a 2BR in Germany for summer, got 2 weeks at HGVC in Hawaii when HGVC did a big bulk last May, Smugglers Notch summer 2X, Flagstaff, 3 DVCs, 3X Pacific NW. All trips were planned at least 1 year out (except DVC), and many were 18 months out. If you strategize and watch the TUG sightings, you can do still get good trades with RCI.