No alpine slide thing on Rigi. I haven't done many of those - we did the adventure park / ropes / zipline thing next to the Pilatus slide - slide seemed pretty crowded on the mid summer day we were there.
Rigi is a lot less crowded in general (except at the very top or when the train pulls in). If you like nice mountain walks it is (in my opinion) one of the nicest places in the world to do that. For more touristy/adventure type stuff Pilatus (or possibly Engleberg?) might be better.